1994 Toyota Camry Transmission slipping, now wont go in rev

The transmission has been slipping for the last week or so - If you start it and go, it may slip into neutral for a second, before re-engaging. My wife lets it warm up first, then there seemed to be no problem when she'd do this. 2 nights ago, she was leaving for work, backed out of the driveway, then started to go forward & it slipped into neutral. Where it stayed for about 10 mins. She drove to work (40 miles) and she called me & said the car now wont go in reverse. She drove it home, and I have had it sitting since. We have the car tuned-up every year, and the tranny checked. This was last done 5 months ago (we always do it in January). We cannot afford to replace tranny now, as we use Tax check to do all tune-ups, etc. Is there something that may be relatively cheap that may be causing this? What do you recommend? This is the very first time we had a problem in reverse.