I did a "best part" conversion several years back. Got a 5.0 for cheap that was the foundation. Also picked up a 5.0 Explorer. Anything that moved (throttle body, TPS, injectors, FPR, pump, etc.) all got replaced and usually upgraded as well. I used a new stock lightening MAF, larger throttle body (later went to the 65mm Explorer for better drivability). ECM was a parts store re-man. All the wear items were fresh, the rest of the hard parts were just good clean stock parts. I have no idea what I spent on it, it was all rolled into building the engine and swapping it into a Ranger. When done it looked like a Ranger with a factory stock 5.0 in it. It was really a mild stroker.
It can be mostly done. Of the few stock parts I used I am sure there over-priced aftermarket items that could have been substutied (Intake, fuel rails, harness) or just generic parts store replacment (ECT, ACT). I am sure I spent less for the OEM EFI then I would have for an aftermarket unit.