I once thought of that too. But it won't work.
Here is why:
1. For example, if you make a model of a sports car, there are other thousand sports cars on that site.
2. People want to buy hi-quality models at the lowest prices. So, to stand a chance, you need to satisfy those two conditions.
3. Selling your car at the lowest price will require you to sell a lot of them to reach 300$.
4. And the bad news is that TurboSquid takes half (that's 50% !!!) of your earnings. So you'll have to aim for 600$.
Bye.