These machines cost $12,000+ in 1990s dollars.

I think it's probably more accurate to say that a version(s) of AIX, Solaris, NT ( and I think a beta of OS/2) technically existed briefly for some models. While some commercial software might have been ported, I doubt it was ever officially supported. Except perhaps some AIX software? I assume it was binary compatible with PowerPC AIX.

Checking https://en.wikipedia.org/wiki/SPARCstation_20 implies that that's a perfectly reasonable price for what it was? The more interesting question is (relative) sales volume I think.

Funny to hear there were ~8 models because my impression has always been that they sold ~8 of them total.