Yeah, my Hasselblad blacks out, but I use it on a tripod and usually lock the mirror up before exposing film, so it's not a big deal. It was disturbing to be looking through the Contaflex viewfinder and have the scene disappear. I think it's one of the reasons the Japanese SLRs became so popular so quickly and muscled the Contaflexes into the dustbins of photographic history. (Besides the Japanese cameras being much cheaper.)
To answer the OP's question, I think my brother eventually sold Dad's Contaflex with both 50 and 115 lenses for under $100. This was a decade ago. I think he got more than it really was worth.