Good question - and the last I checked kbb and edmunds didn't have used pricing guides for the 3 yet.
I agree with BlueMonsta...I'd be suspicious as to why the current owner is selling it so soon after gettting it. This doens't mean it's not worth checking the car out. You could get a carfax report done on it to see if it's been in an accident. If you have a mechanic you trust you could also see if they could check the car out for you.
I think you could get a new brand new one for about the same price. Here's why: If those are the only options on the car the invoice price for the car new should be $15,250. I got my car for about 250 under invoice. You should be able to as well, and if you play your cards right you may even be able to do even a little better. Since the dealers will need to be moving there 2004 inventory they may be willing to make some deals (if you're patient) over the next few months.
The price they're asking is probably what you'd expect to see. They'll probably say that the car new would be $16k+ quoting msrp. However, this isn't relevant since you shouldn't have to pay msrp even if that what they happened to pay. I think the car needs to be marked down compared to what you could really get one for new even if the car has had no wrecks and was well maintained considering:
1) You'd be the 2nd owner so the car would be worth less than one that you were the original owner of.
2) This car has 5000 miles on it which makes it worth less than one with next to no miles on it
3) You'd have 5000 miles less warranty, and probably a few months as well (most likely its the miles that will run out first on you)
4) You may not be able to get as good of financing on the used car. Mazda is currently offering 1.9% on the 3 I think, though you'd need to check to see if you qualify. This beats the 2.9% I got through a credit union (by the way some banks/credit unions may be willing to treat this slightly used car as a new car loan considering it's year and mileage).
I wouldn't rule this person's car out, but shop around both for financing and for a comparably equiped new one. Good luck. By the way, I'd like my hatch but I wouldn't mind having a 3i 5speed since it would be a very economical yet fun car.
