www.6gc.net
The reason for the horsepower discrempencies is cus of California

Damn California. Their GTs after 1996 come with different hp ratings; torque is still at 145, but hp is down to 130.
Anyway, goto 6gc.net for more information. (No offense to anywhere here at TN.com)
A turbo setup can be had for as low as 1200; but it'd only net you 220 or so hp; More than that and you're looking at 3000-3500; which isn't bad, because if you're real crazy, you can do a 3sgte swap after that and move all the turbo stuff over.
Here's a couple links to turbo'ing the 5sfe:
http://www.6gc.net/forums/index.php?showtopic=5574
http://www.6gc.net/forums/index.php?showtopic=14345&hl=
No one has EVER done a RWD or an AWD swap into the 6th gen celica chassis. I've heard of one person doing it in europe... but they have easy access to real GT4 parts.
An MR2 tranny won't fit the ST204 chassis, but it's 3sgte engine will. The 6th gen celicas GT transmission works with a 3sgte just fine