Is it worth putting a transmission in a 1992 mazda protege?

Hello
Without adding any options, Kelly Blue Book puts this car's worth at about $1400.  You can try for yourself at http://www.kbb.com.  
Whether or not it is worth putting the transmission in depends on the condition of the car and how much you enjoy it.  If it's a good car (which it seems it is by the engine running well and the body being in good shape), then updating the transmission can help it run for a long time.  If not, it could start nickel-and-diming you.
Best of luck!
CarGrrl

500 is a little pricey, but it is definately worth replacing if its in good shape. i have a 93, and it saves a ton on gas.

If you can find a donor car with the manual, my 1992 Protege DX gets me an average of 33mpg.  That's primarily town driving, with about 20 minutes of highway round trip from work at 60-65mph.

I know the automatic, with it's fewer ratios and increased loss due to slippage gets less overall mileage, but either way, I'd say it's worth getting the transmission fixed.  A decent shop should be able to rebuild your existing transmission cheaper than buying a used one and rebuilding it and replacing it.