Hi Steak, a great option may be this ... and it is reasonable. M&R Electronics is reputable ... this link (
http://mnrelectronics.com/par16delolam.html) will take you to the OEM Radio/Cassette Deck like the one in my 1990 for $124.00 ... if your Reatta does not have that unit I'm sure they have the correct one.
A less glamorous option may be a salvage yard if cash is tight. When I had the Reatta I had before my current one the Cassette Deck went bad. I went to a local salvage yard that does their own pulling. They had several complete units ... three of which were in tiptop shape (the others not so much) ... $15.00 and 2 hours later I was back in complete AM/FM/Tape operation ... returned the core for $2.00 refund. Apparently the unit was used in a number of GM autos therefore not rare.
See ya, John in Sarasota