The 6C is likely the most reliable of the Kievs. It's alot simpler then the 88s. The only real issue is frame spacing and worse case you can adjust that yourself. The advantage of the Kievs is you can build yourself a collection of lenses.
If you only want the 80mm then I'd go to Keh and buy a Bronica SQ or a Mamiya RB67. If you can live with 6x4.5 I'd buy an older pentax 645 and a Kiev lens adapter. You'll want the adapter to fit the Kiev fisheye at the very least.
Having said if the camera is in working condition and the price is less then $100 it wouldn't bother me. Personally I'd rather have the waist level finder.