I've spent anywhere from $6500 to $7500 on my 20v conversion and that's with NO labour.
Honestly though, if I were to do it again, I'd be starting with an AE71. Either that or just a different motor. BEAMS, SR20 etc.
4AGE's are considered an easy conversion but for the messing about I went through with the W55 box, I may aswell have chosen a different engine.