I just dealt sunroof cable thing - like most e9 issues, there is a trick.
The stock sunroof cable attaches to the roof with a plastic block. I'm going to bet that your plastic bit has broken, and you've found that new cables cost $160 apiece.
Mid 80's Volvos used sunroofs made by the same company (Golde), but their cables use a metal block. You can find these cables in wrecking yards - they are a bit long for an e9, but shortening them is not a big deal.
I'm sorry, but I don't know the exact Volvo model that uses these cables. But, it's worth disassembing a few Volvos at your neighborhood wrecker to a) save 2 X $160, and b) get a better part.