For comparsion purposes, I've seen 2003's from $27k to $37k depending on mileage/options.
to do a search on used bimmers at Edmunds.com.
You should be able to find some 2004 CPO's now to see how the price is going.
2004 E60 530is, Delivered 12/12/03, TiSilver/LGrey, PP, SP,PS, PDC, ACC, FRS, Step, Xenons, clear bra, body colored rear inserts. (Retired, 1983 henna red 320is)
2004 Corvette Z06 Commemorative Edition