it's not the most financially sane decision.... but you are only young once
just remember that your car payment won't be your only expense
tripple the gas $ you spend now, call your insurance and get an exact quote on how much your new insurance may be. it may not be that bad
I only pay $1400/ year full coverage and I'm 23
But, regardless, I don't think you can afford to buy a M3
Since you mentioned that you don't drive much, you may want to look into leasing.
This won't work if you plan on buying the car though (as lease-to-buy isn't usually favorable when compared to a straight finance)
a gf will cost you $, but not all that much
I guess since my gf is someone who is independent (I wouldn't say feminist...lol) and doesn't like to have everything paid for, so my expenses are minimal (i actually think she spends more on us than I do...by a considerable amount).
So you may or may not want to count the gf as part of the equation; depends on your/the girl/etc
if you want to buy used, then wait a little more for the new gen to come out.