Coupe Transmission on the Fritz

[aspeer@mail.utexas.edu (Andrew J. Speer)]

How could I put this more succintly?  HELP!!!!!
I was just driving back from Barton Springs (great place to go for a swim if
you ever come to Austin, but I digress) when my '84 Coupe GT shift lever got
stuck in 2nd, I managed to get it out but found from there I had no shifting
whatsoever.  I just had up and down, and no sideways play on the stick, no
gears would engage.  I was stuck in 3d gear and the clutch was working fine.
Amazingly I was able to drive home (what was that I heard about even
mortally wounded Audis never stranding their owners?) through stop-and-go
traffic and a couple of red lights on pretty steep inclines (I wonder what
the people around me must have thought when they heard this wildly revving
engine getting started on an especially steep slope - thank God, I mean the
Audi gods, for low gearing! =)

OK, so the big question is WHAT HAPPENED?  Are there a myriad of
possibilities, or is it most likely something clear cut?  Is my mechanic
(normally a reasonable fellow) going to hit me with a massive repair bill,
or is it something relatively minor?

Thank you very much in advance,

Andrew Speer.