[84LX89GT]

I would go for the 89 5.0 Convertible, you won't find anything drivable without major problems for $1500 otherwise. I bought my '89 for $1500, but i ended up doing alot of work on it (most of it voluntary for modifications) because it was an older car with 114,000 miles on it.
If you try and buy a newer model mustang most of them are still pretty expensive because depreciation hasn't caught up with them yet and by the time it's paid off it'll be worth quite a bit less than what you buy it for. I love my '89 because it has a 140mph speedometer, 5 speed, already had quite a few modifications when i bought it and is easy to modify because of the relatively low cost of aftermarket parts (which are about 1/2 as much to buy than any import crap on the market).
Just imagine, being in high school, with a fast 5.0L convertible.....can you say chick magnet
No matter what you get, just remember these words of wisdom based on my experience as a dumb testosterone driven teenager (i turned 22 earlier this month):
1. Don't screw around AT ALL in the rain, the rearend will fly around faster than you realize what's happening. You can get away with it a deceptively large amount of time...it only takes one loss of control to hit things.
2. Literally don't waste gas racing people on streets, speeding tickets will hurt your pocket book, racing tickets will get your license taken away, losing control.... very easy to happen and might injure you or someone else. I'm addicted to racing at the track now, there's no chance of getting a ticket and you have numbers to back up what you say.

You don't have to listen to any of this, but i am talking from experience of having 3 at fault accidents with one 19 over ticket, please be safe no one wants to see another mustanger get hurt

Anyways, good luck and i hope you get a stang you can enjoy for years to come!