The convertable is a POS IMHO but then I hate all convertables. Volvos convertable is or often can be a very problematic car and without descent structural support being FWD, suffers from what's called "cowl shake" which makes it seem as though the whole front end is loose, steering wheel vibrates.
The coupe is OK, just like the S70s EXCEPT for one major weakness, the poorly designed, contructed window regulator assemblies (same in both C70 versions). By design, they will all fail eventually and when they do it gets very costly to replace that regulator. It's also a job that requires a tech with experience as for any guy trying it the first time, it never goes back together correctly w/o many problems like proper fit, wind/water leaks.
I've bought a car on Ebay and mine was worth the hassle of traveling for. I got on a plane, flew 1000 miles and drove my car home. It was a fun adventure and I'd do it again for a unique car that I really wanted.
I'd keep looking for your 850R as they're out there, even though probably not often up for sale.
If you know anyone in the used car business, preferably at a Volvo dealer, they might be able to help you locate one?