Slipping Automatic, Rebuild? or Get a New tranny?

[1LoudSHO]

A car I'm severly interested in (94 SHO ATX) slips in the 1-2 shift, and other times too. How much should I be looking at to get a newer Tranny for this car? and should I rebuild or buy a completely new one.

Thanks guys!
1LoudSHO