I have a 1999 Ranger that was a little beat up but ran well until the transmission quit on me. Anyone know what it will cost to put a new one in and whether it's worth it?

 

Depends, can you remove the trans and replace your self? If so it opens up several options;
1- buy used trans from salvage yard and install (possible you will be do it again) cost under $1000 total, trans it self could be as low as $300, plus fluids and filter.
2- remove current trans and take to shop for rebuild (better as you have a good trans) cost just over $1000
3- Take to shop and have rebuilt (best they will warranty the job) in the range of $2000
4- have trans replaced with new (costly) in the range of $4000

Good luck