There's a lot of Cyclones and GT7's floating around that go for around $50 or so that are great speedo's and will handle most anything you through at it.
On a side note, before you go out and buy a low turn hot mod, keep in mind the maintanence involved in running one. The few times I raced mod the comm needed to be cut a minimum every four runs and have the brushes replaced. If not racing you can go a few more but you begin to suffer problems of poor performance, further accelerating brush wear, hung brushes (causing you to roll to a stop), and shorter motor life.
A 19 turn motor is one that delivers great performance and can go up to a couple dozen runs before major maintenance is needed. If faster is what you're after look into brushless setups that include a motor and esc. They'll be quite a bit more up front, but they're almost maintenance free.