At least you realized in the end no matter what you do to it, it's still a Civic. You're waaay ahead of the game with that epiphany. For under 20K, the only "sporty" things I can think of is:

1. Miata (used)
2. Neon SRT-4 (used)
3. WRX (used)
4. Mustang (used) (i'm pushing it here)
5. 240 (obviously used)