IMO, the Ofna Hyper7, or Hyper PBS RTR are good buys. both offer good reliability and lots of upgradeability and come with a great engine for racing.
This said, the most common cars at my track by far are the Kyosho mp7.5 and, to a lesser extent, the Mugen mbx-5. These cars are purebred racers and the cost reflects this, but if you take care of your car and maintain it well any car you chose should be relatively similar in price racing over a season.
good luck choosing your car.