I just replaced the head unit in my 83 SC with a new Blaupunkt Toront BT400. Purchased via amazon Germany (Amazon.de: Günstige Preise bei Elektronik & Foto, DVD, Musik, Bücher, Games, Spielzeug & mehr). After all shipping/for-ex fees it was within $200. It has all I need --- UBS, in-line Aux, Blue Tooth and CD. Very subtle classic Blaupunkt look --- with a big blue lighted button (on/off volume)!
There's a newer BT420, but it is ~ $80 more. It will give you SD Card functionality.