My son may have a Bose cd/cassette deck for sale out of his 94 Seville STS. Not sure if it's the same or not, but if it is, he might be willing to sell it. He also has the front speakers for the bose, but the top piece of the case has been modified for an aftermarket speaker. Let me know if this will work and I'll ask him what he's willing to sell it for.
If what you have is a non working unit or a factory tape deck I BELIVE the dealer can swap it out (parts only) for $200, my mom's cd player stopped working and they told her to bring in the old one and for $200 they'd give her a factory exhange unit (probably rebuilt).
I have a working Delco (non-Bose) cd/cassette HU from a 2002 Seville SLS. The part number is 25739872. If you determine that this will work in your car, I will take $80.00, whixh will include the shipping costs to Rocky Mount Virginia. I have a Paypal account, or you can mail me payment. Let me know if you are interested.