The pickings are incredibly slim under $7k in my area, so here goes:
$3500 212,000 miles ish on body before I decided to beef my car up. I had the engine built from a new block from ford. Everything in it is new. I do not even have 3000 miles on it since upgrades. The
killeen.craigslist.org
First candidate, $3500. Lot of receipts for work done, though most of it is for stock parts or minor upgrades, she's a maaco paint job away from being a 20-footer, but for the price... even the Mustang II guy here is tempted.
Excellent Running and Driving Mustang. Our Mustang was completely Inspected in Jan. 2018 to Repair and update for long term use. The upgrade and Repair was $2143. Call for the List. This one needs...
austin.craigslist.org
My second choice, a super-clean 2.3 LX hatch for under $4000 that is begging to be Coyote swapped. I mean seriously... I can hear it calling to me...
1991 mustang for parts or a fixer upper. does turn on.motor is in great condition.no knocking or smoking transmission grinds when shifting from 2nd to 3rd above 2200rpm it is missing hood and seats....
austin.craigslist.org
$1200 5.0 that runs? I mean, it's kinda trashed, but I know where there's a hood for less than $100, and Mustang II seats fit a fox, so I'd steal one of ElSuperPinto's to drive it home if it was legitimately otherwise driveable. I've bought worse at around the same price.
GREAT PROJECT RIDE HAS THE 5.0 AUTOMATIC TRANSMISSION COME TAKE A LOOK AT BEAR COUNTRY AUTO SALES! $1295 plus tax and title transfer call me for cash price out the door! This vehicle is located and...
waco.craigslist.org
1985-1986 GTs are my absolute favorite fox-bodies. Seriously, if tomorrow there was some asinine California-style law passed that outlawed owning and driving vehicles older than a certain age (they've already done it for diesel trucks), and the mid-80s was the cut-off... they would be my first choice for my classic car to

around with when I felt like it, and this one... It's been there for awhile, I bet cash would let me haggle it down from that $1295 asking price.
1991 mustang gt. Bored 30 over, all trick and flow. T3 gear,New battery,tires,fuel rail. Engine and transmission rebuilt. New paint. New tires. Daily driver. Has complete nitrous system. I removed...
dallas.craigslist.org
This one is technically my answer to Noobz's question... But... I hate the wheels, I hate that it's an AOD, and I hate the fact that it's got nitrous, but it's otherwise pretty clean, and right at our $7000 limit for this exercise. I personally probably wouldn't buy this car, at anything above a gimme price, but it's the only one that meets Noobz's criteria, so I included it in my findings.
1987 Mustang w/ 5.0 high performance, manual 5 speeds Aluminum heads Headers, I'll be answering texts only.
dallas.craigslist.org
$4500, but can't be bothered to provide details other than it's a 5.0/5spd with headers and aluminum heads?
If I had to pick which one is actually the best???
I'm thinking the 2.3L car. I know it hasn't been abused too badly, it's very clean and un-**** with, and I'm going to coyote or 4.6 4v swap a fox if I buy another one, so which engine's in it doesn't mean much. Under $7k doesn't buy you a clean 5.0 fox that hasn't been **** with down here anymore, too many guys from up north coming down and buying them is jacking up the price. Hell, it won't even buy you a clean V8 Mustang II anymore. There were two carbureted cars I wouldn't touch with a 10-foot pole around $7k. All of these but that basket case '91 and the 2.3 car could be made into a $7k car fairly easily.
I know that really wasn't the question, but seriously, everything else was $10k plus down here that wasn't trashed and nowhere near worth the $7kish asking price.