There is a GMPP, TCI and other standalone computers that will comtrol teh electric 4l80e trans.
there are also full manual shiftkits that will allow the use of teh 4l80e WITHOUT any computer at all. PATC offers a manual shift kit for sure.
You have to shift this kit manually. If the selector is in 3rd gear, the trans is in 3rd gear, even at a stoplight. With the manual shiftkit, you will lose teh TCC lockup function however.
I have seen teh TCI computers go for $350US on ebay before. These usually drive a 4l60e AND 4l80e trans.
Compushift also makes a 4l60e/4l80e trans control computer is also in the PATC link.
Here is some info from PATC The manual shift kit is about 1/4 way down the link. Its listed at $295