HiCustomerand thank you for using Just Answer!
You have a couple of option that might work and might not work, if you want to try them. You can service the transmission, lowering the pan and changing the filter and fluid. This is an outside chance of doing any good, the newer fluid may help in the slippage and it could even make it worse.(I have seen this before). You can buy a conditioner and add to the transmission, this also is an outside chance.
I wish I could tell you there is something that could save the transmission but once they start slipping it usually is matter of time before they fail completely, even if the things about help some. One last option that might be chaeper than a rebuild is call around to the salvage yards and see if you can find a cheap transmission. They sometimes have low mileage transmission for alot less than the price to rebuild. In my opinion to rebuild you are looking at $1500.00 minimum.
If I can help you further please let me know.