Buy a 5.0 Mustang for 5k, a trailer for 1k, and use the rest to learn how to set up , tune, and run consistently. You'll burn through money faster than you ever dreamed possible just getting your feet wet the first season. If after that first season you have got the yearn to burn, then you'll know what it costs to continue the next year. (Which starts immediately after the last run of the FIRST season!!)
You blow your whole wad on JUST a car then you'll be sitting out the whole of the racin' year.