I remember i was just looking around to get some prices last year on an engine swap... too expensive for me... but here is what a local tuner was suggesting for pricing (
www.cgmotorsports.com - CG motorsports in BC, Canada):
Below is a list of options you can choose from, prices include all
necessary parts and labour. Taxes are extra.
-2.0 L 6 cylinder motor conversion (from 320I), 140,000km $5,200 (~3900 USD)
-2.5L 6 cylinder motor conversion (from 95 325I), 95,000 km $7,200. (~5400 USD)
-2.8L 6 cylinder motor conversion (from 97 328I), 140,000km $9,200.(~6900 USD)
-3.2L 6 cylinder motor conversion (from 98 M3), 71,000km $13,500.(~10125 USD)
....These are prices from last year, and as stated above include all the parts and what not... not too bad I guess, although I don't have over 14 grand to spend on that... and if i'm going to do a conversion, why not go fro the m3 engine, and not to cheap out and go for a 325? if you're gonna do it, do it big the first time.