I'd assume at least a $2000 dollar or more premium over carbs. Remove price of carbs, but same motor, manifolds, et al. But you'll need a fuel return to the tank, high pressure fuel pump, injectors, fuel rails, pressure regulator, high pressure fuel filter, coilpack, and injector harness and all sorts of connectors,
Besides the crank trigger wheel and VR sensor for spark and fuel triggering(unless you have a cam sensor then it's times 2) you'll need a few sensors:
IAT: Intake air temp, seen above in top of air cleaner
MAP: manifold air pressure, usually on board EFI computer
TPS: throttle position sensor, comes with Weber-looking throttle bodies
CHT: temp sensor for coolant on watercooled or cylinder head for aircooled, controls warmup mixture as well as cold and hot start fueling
VR crank: variable reluctance sensor uses a toothed wheel with one missing to signify TDC, this allows batch firing injection and wasted spark ignition. To go full sequential requires a cam sensor which will give you TDC for all 4 cylinders
Wideband O2: this is usually used for closed loop, real time mixture correction to keep it in the intended range.
Sometimes there is another MAP sensor for reading the barometric pressure: i.e. altitude mixture compensation.
I may be going this route someday. I have a set of CB throttle bodies, injectors, rails, fuel pump, and regulator. I just need the brains of the operation. that would be electronic and ummm, mine!