I'm going to try to tread really lightly here-- because I'm a retro-grouch who's biases and opinions are well known to long-time SOC veterans, and because discussions of money on this site always seem to descend into places that aren't really productive to go. I'm hoping I can throw a couple of things into the mix that might provide some clarity.
The weak link for 99% of the people trying to enjoy these cars is the power-train. The original concept of using a Type 1 VW platform for mechanicals was genius back in the 70s when Frank Resiner designed the first speedster replica. At that time, there were many tens of thousands of beetles running around, and at least one "foreign" (VW) shop in every town in America. Stuff was stupid-cheap, and nobody expected as much from their cars mechanically.
That was then, and this is now. 50 hp isn't so fun after a couple of years, and in many swaths of this land there hasn't been an ACVW on the road for useful transportation in 25 years. VWs used to burn to the ground with regularity-- and even when they didn't, they oxidized into powder in less than 10 years. There's never been an ACVW with decent heat. VWs are still used in niches out west, but east of the Rockies they are obsolete novelties.
Guys like Vince M. don't want to talk about mechanical stuff on this site because they don't have to. Guys in most places besides So-Cal HAVE to know and care about this stuff, or their cars will just become garage-art.
Still-- the replica speedsters held their appeal everywhere (not just in Kalifornia), even as the platform they were built upon on became increasingly obsolete everywhere else.
There are 3 commonly used power-train families used in 90% these cars: Type 1, Type 4, and Subaru 4.
The Type 1 is still far-and-away the most common, because the aftermarket is still reasonably robust, and because they lend the illusion of being economical. The problem here is that the law that says, "affordable, powerful, reliable- pick any 2" is immutable. Almost everybody defaults to picking "affordable" and "powerful", and the cars become something of a fair-weather toy to be enjoyed within 30 miles of your front door. A "reliable" and "powerful" Type 1 is not inexpensive. Horsepower/dollar, it's certainly more expensive than a small-block Chevy or Ford, and probably approaching the Porsche end of the register. Even with an essentially unlimited budget, and a willingness to go well beyond "normal" or even "rational", a big Type 1 remains more highly-strung than most guys are willing to live with. I really like this, as I tend to favor stuff that is at the end of it's evolutionary cycle, but most guys can't live with it at all. Even I am in the process of detuning to some extent in an effort to give up some h/p for a bit of reliability. There's a sweet-spot with a Type 1, and it's about $8K and 130 hp.
A Type 4 is quite a bit more reliable as long as a guy doesn't reach much beyond the 150 hp range-- but it's not cheap either. Type 4 stuff was never as plentiful as Type 1, and there are probably less than 100 guys in the world who specialize in them. That being said, at least the air-cooled Porsche shops will work on them, as they are 914 engines. They resolve many Type 1 issues, and parts are generally of better (and more expensive) quality. If I'd have had a lick of sense, I'd have just written the big-checks all at once, and done a big Type 4. Rich D. has a 2.8L Type 4, and I can tell you from experience that it is an awesome thing, and certainly WAY more reliable than my (claimed) 200 hp Type 1 ever was. Still, they are old-skool air-cooled, and require monitoring head and oil temperatures closely, provide no heat, and generally give off a retro-racer kind of vibe. You can't just jump in and drive "anywhere"-- you plan, and take some spares.
The Subaru is not like the other options at all. It's modern, powerful, and inexpensive laying there in the salvage yard. However, if a guy wishes to retain all of the modern goodies (EFI, etc.) they are far-and-away the most complicated of these power-trains to install in a speedster. I'm sure there will be dispute about this, but it's the truth. The wiring harness alone is a nightmare, as systems in modern automobiles have become more and more integrated with each other. Keeping that factory EFI map, and OBD2 capability might mean you need to rat-hole instrumentation from the dashboard of the donor car somewhere inside your retro-appearing Speedster. You have to figure out where/how you're going to mount stuff, and where you're going to adapt to the VW running-gear (Porsche transaxle? VW? Subaru with a special R/P?). A water-pumper can provide real heat in the cabin, but that requires a bunch of fabrication too. David S.'s way of doing this is really, really smart IMHO-- sacrifice all of the electronic wizardry that provides instant start-ups in any weather, etc, but retain the excellent mechanical reliability of a modern Japanese power-plant. Yeah, it's got carbs (and the attendant idle-jet issues, etc.), but it's as simple as this installation can get. He could always put his throttle body back on, and control it with mega-squirt if he had a hankering later on. He's also got less in his stuff than most people do in a really bad Type 1.
There are other options too, which present alternatives that most people don't consider. Early 4 cyl (pre Type 4) Porsche stuff was always considered an ignorant waste of money, as the parts were expensive and the performance no better than a Type 1. But these engines were always weighted towards the "reliable" end of the spectrum, and the quality of parts available for them makes them really interesting to me (as long as something in the 100- 120 hp range is adequate). A guy can buy a Tangerine Racing tri-Y header for an early 912 engine-- and other really, really nifty parts. They can be built to 2L or so. They aren't drag-racing motors, but very few of us are drag-racing.
Intermeccanica does a 911/6 car. On the surface, this sounds like an insane waste of money-- but I've driven a couple of these cars, and they are quite nearly perfect. "Awesome" is an overused adjective, but there's a picture of an IM/6 in the dictionary under the listing "Awesome". 200+ h/p, an exhaust note that is like no other (OK, perhaps a Ferrari 12 is better, but cummon'), and 200K+ mi reliability. Rick Davis drives his like a normal car, which is to say "everywhere/any time". When you jump on the throttle, it sounds like the sky is ripping in half. The cars are all Porsche- transaxle, suspension, wheels, everything. There is no VW compromise left in it. If I could choose any car in the world to own-- it would be an Intermeccanica Porsche 2.7 Roadster with dual-plug heads, all the updates, and PMOs. I'm not kidding-- these cars mash every single one of my buttons.
There is no "best", as everything represents some compromise. How much money is too much? How much power do you REALLY need? Do you want to win drag-races, or drive across the country? You need to decide for yourself, with enough information to make a good decision. There is no short-cut, no secret-sauce that all the smart-guys are doing, and nothing you are going to think of that hasn't been tried by somebody somewhere. Peter must be robbed to pay Paul-- how much is something every man decides for himself.
Forewarned is forearmed.