ExtraCortex, make package from 10-20 tires. Reduce polycount to 1000 (200 or less even better for simple tire, i saw 6sided tires in many good commercial games). Provide different textures for each tire (bumpmap texture are welcome too).
Well, after that $10-15 is a reasonable price. At the end: you can open small web store with tire packs (for different cars). That's a point, i think.