I guess then it would all depend on the condition of the outter rim itself. Is it in good condition, without any major bends or damage and just needs to be trued, or is in bad shape and need to be replaced?
If it's the first, I would suggest taking off the rag joint, and either true the wheel yourself, you can buy a good spoke wrench for $10, it is a useful skill to have, if you broke spokes once, I can guarantee it will happen again. I have had to do it at least half a dozen times. OR you can take it bike shop and have it trued. I have had mine done for as little as $10, but it depends on the shop.
If it's the second it may not even be worth repairing. The cost of parts on labor to repair low to mid end bike rim is not worth it. One option may be to go down to a thrift store and see if they have any bikes that you can buy cheap for the rear rim. Not to mention you would have a spare parts bike for anything else you need. Or buy a new rim from a bike shop. If you go that route make sure you get one with heavy duty spokes on it.