Is there a lot of 'play' in the shifter itself? I had a car that happened to once, and it turned out that there was a $4 part that it needed. If the shifter seems sloppy, it could be the nylon bushing that goes into the tranny. If that bushing goes bad, it might cause the car to not go into gear. Would hate to see someone spend a bunch of money on something they might be able to fix for a few bucks.
Good luck, Tommy!