Just out of curiousity, I was asking a friend of mine (owns a major dealership) what my own car was worth, so I asked him what a 2002 A4 1.8T AT- 88K would fetch on trade. He said if the car was clean and he could basically resell it as is, he'd buy it for about $16,500-$17,000. He also said that it didn't make any difference what you bought from him, he'd be giving you the same. So, if you bought one of his $19,000 Mazda3's, you'd get $17,000 and simply pay the difference. He's had lots of people move from more expensive cars into a Mazda6 or even Mazda3 and cut them a cheque for the difference between the new car, the buyout, and the value of their existing car.
Anyway, I'm not sure what the car would retail for, but I'd bet that $17K or so is a fairly accurate wholesale value, at least in the Edmonton area...