There are a couple of issues here.
Replacing / rebuilding the transmission should cost less then $2000. You have to check with the local tranny shops in your area to get a real number. The cost is usually less for a RWD car than a FWD car. If the exhaust system is in the way of the job and it is rusted badly you might have to add a new exhaust system to the bill. If you plan on keeping the car for a long time you might want to get a crate tranny from Ford. Later versions of the tranny have stronger internals. see the tranny section under tech articles of
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for more details.
Should you keep it or get something else cheap ? Is there anything else failing on the car ? head gaskets ? heater core ? rust thru ?
If you bought another car in that low end price range you are replacing a car with known problems with a car with potential unknown problems. How much are you willing to spend on the new used car to get that one to a usable point ? Example: a few years back my mom bought a used one year old Sable wagon off a dealers lot. It was a turn in from a corporate fleet. Even though it basicly seemed ok at time of purchase she had to bring it back numerous times for reprogramming the computer for driveability issues, blown speakers, and a significant hidden water leak (cracked center brake light housing) that left about 20 gallons of water under the third row seat after big rain storms.
new or different is not always better, sometimes you get lucky, sometimes you don't.
Steve