Very cheap, very small, sort of powerful 3 ch amp

Thanks for the responses. I hadn't actually thought of bridging a six channel amp. That approach seems to pose a problem though. My understanding of how bridging works is that it halves the impedence that the amp sees. In fact, the Rotel RMB 1066 states that in bridged mode, the amp can't handle anything lower than an 8 ohm speaker (presumably because it's actually trying to drive 4 ohms bridged). My center and surrounds are all 6 ohm nominal and I don't know the impedence curves so I don't know what they dip down to.

So I think, in order to successfully bridge, I'd have to find an amp that's happy driving a 3ohm nominal load for my speakers. I'm assuming that I should listen to the manufacturer and that the Rotel rmb 1066 wouldn't cut it here? Too bad as that's really an ideal size and price.

AMC 2n100-3
I don't know the seller, but these AMC amps used meet your specification - cheap, small, sort of powerful (150 w/c).

Another 6 channel Rotel "bridger" here the RMB1075 is around $700 new so I am sure used would fit your budget, I ran this bridged and in 6 channel mode and thought it wouldnt be enough power, even at 60w per channel I never needed anything more (for movies).

Look for a six channel amp and bridge the channels to get three (more powerful)channnels. I did this with a used Rotel and it sounds great. There are switches on the back of the amp to bridge the channels.