If the car is documented for the mileage and in really solid condition, that's an almost absurd price. Beater Miatas sell for $2000-2500. Seriously. The hardtop alone is worth $1500.
A good condition rust free car can usually fetch $4000-5000 without much difficulty, and a pristine car with a hardtop, summer only driving, and good records can fetch as much as $8000-9000. Seriously. A friend of mine sold his for over $8K in the spring. I had offers of $8000 this summer for mine, probably could have got them up a bit had I been selling.
