If you are 5'8" or smaller, Miata and Lotus are a barrel of monkeys. Much taller than that and they get tight real fast.
For the lowest cost track days in a reliable car find a used Toyota Corolla and hit the Lemons circuit. A ton of fun.
For a dead nuts reliable Porsche, go 2009 and later. All the weaknesses of the 1998-2008 cars have been engineered out.
