The cost of rewiring is crazy for this project! You'll need to rewire AND replace the Cassette Head Unit. Don't even begin to ask what that will cost. This project will cost thousands.
Why bother? Just buy the up to model year 1998 CD changer, available from your dealer. Or spend even less, and buy an Alpine CD changer and wiring adapter. The latter of these options is just a few hindred dollars, easily paid for by selling the optic CD changer.
1998 C230 "Black Betty"