u will drop a valer in for a grand...ok, here comes the break down

1.8 16v lump will cost about 250 max with gearbox
2.0 16v 9a audi lump will be about 350 max
150 mkII 16v box
wiring u can get from TSR for about 120
and downpipe is about 100-200
Gains, a std 1.8 16v lump is 139 bhp a 2.0 is 150ish (and loads of torque)
For a cheap and quick turn around i would chat to Jody from Dubvelopments, he has done LOADS of mk1 16vs and is very helpful, email me for his number but im sure he will give u a good price for a drive in drive out conversion.
i went all the way with mine and fitted a flowed head, oettinger inlet cam and twin 40's. the result was 168 bhp, 140 lb/ft. a fresh 16v box with LSD made my car fly...esp on the track
hope this helps clart