Honest to god prices would say a r33 rb25det 5 speed is worth $1500 second hand any day of the week, with some sort of warranty. Allow at leat another 1.5k for stuff as mentioned like pedal box and lines, clutch and flywheel, new flywheel nuts, gear box crossmember, tail shaft (or modify exsisting, around $350 mark last time ive done it) manual shifter surround, gear knob, and then labour to fit, dont forget reverse and neutral switch wiring, and thats for the standard gear. if you want a decent clutch and flywheel, id say costs would be around $4500- 6000 depending on clutch and how complete the conversion kit you get is.
Ive always found cars converted from manual seem to be better cars, maybe because they have had a easier life and bought by a different type of owner from new. Both my S13 were autos converted, were at the time a lot tidier than others that i looked at.