I think the two output tube Sunns have been hanging out in the $450 - $550 for a while now, maybe a year or more. I don't pay a lot of attention to the transistor amps, but a quick scan of ebay sales looks like they are in the $350 - $400 range, which I think is higher than they have been in the past.
I do remember when Concert series regularly brought $100 - $200 and it doesn't seem like it was all that long ago.
A Coliseum 880 recently went for $1000, but one sale could always be an anomaly. That sounds like a BUNCH of money for an old transistor Sunn to me.
I've also noticed that Betas seem to often bring more money than I think they should, and as you say the preamps sometimes bring stupid money.
Of course, about 20 years ago $500 would have bought you a truckload of old Sunns, both transistor and tube! If I only had a time machine...