FSM = Factory Service Manual

For a fuel only megasquirt, you're looking at sub $300.
Other parts required:
High pressure fuel pump (inline)
Some form of GM TBI ($50)
Adapting the TBI to the stock manifold... Think Toyota -> Holley -> TBI (cost ??)
02 sensor ($50)

You're still on the hook for tuning and wiring, but I think that's the case for "painless" fuel injection also.

Another option is a slimmed down 22RE harness - at least 2 vendors over on pirate sell them, but the cost is in the $400-$500 range and you'll still have to find the EFI hardware (pretty cheap) and a good 22RE head... www.celica-gts.com - guys over there have early 22r heads setup for EFI...