I assume manual trans?
It will be a Toyo Kogyo trans but could either be a 4 or 5 speed, used from '83-'87
Look at the Drivers Door sticker and find the Trans Code
X = 4 speed
5 = 5 speed
You would rebuild the transmission or do an exchange for one that is rebuilt.
You would need to call local transmission shops for pricing.
Here is a site that lists cost of rebuild kits, so you have a general idea of cost:
Ford Toyo Kogyo 4 & 5 sp Rebuild Kit Manual Transmission - Drivetrain
With that old of a transmission I would be leery of getting a used one without rebuilding it.