A $1500 miata with 949 big grip kit and 15x9 wheels with some good tires is honesty the fastest and most reliable thing for that budget. Other than that you are paying to be more unique.
I paid 3500 for my super clean 90 miata. Put energy bushings, used koni yellows and ground control coilovers on it. Used 15x7 wheels with used hoosier SM7s and the car is capable of doing 1.48s at midohio club. That's less than $5k and less than 100whp.