1993 Ford Escort Not in gear

Today the car began to feel like it wasn't in gear as I was driving it. I would stomp down on the gas and the car would lurch then the problem would stop. But, as I drove further, the problem began to happen more and more often. I got home, called my husband, and he told me that all it needed was a tune up and it was still drivable. I had an appointment this evening, so I started the car up and less than a quarter of a mile down the road the car really did pop out of gear and would only rev in neutral when I pressed the gas. I turned the car off, turned it back on, and it went into gear again, so I turned around and took the car back home. What is the problem with the car and what is a ballpark figure on what a repair of this kind would cost (a breakdown on the cost of parts-new and used- and the cost of labor)? Thank you.