240 auto transmission

I hae a '92 240 auto. It has a serious problem that I think is the transmission. When I was driving it suddenly lost any power as if it had slipped out of gear. The engine continued as normal but we were not going anywhere. I managed to park and after resting for a while it engaged gear again and I was able to limp home by stopping/resting/starting. There was no warning that this was going to happen but in hindsight it may have been more sluggish than usual in the days before it happened. I have not driven it more than a few feet since then but have started it and am able to move it back and forward in gear. I am assuming htis is expensive problem and need to get the money together before I take it in for repairs. Can anyone shed any light on what it might be that has brought this on? Thanks in advance