It seems a little on the low side, but that might be because the zhp is a little less common, but things like this can vary. My advice is to remind the dealer that the E90 is coming out in the 2006 model year, with updated engines, you might also want to ask other dealers about what they would discount.
If I were personally in your shoes, I would either wait for the new 3-series to come out (the 3.0 has 260+bhp), but I dont like the styling as much as the E46, or... Get a slightly used M3. You should be able to get a 2002 or a 2003 M3 w/ 10,000 miles or so for about the same price.