Low cost Amp?

An Amber Series 70 if you're OK with 70 wpc.

Any number of Parasounds.

Personally, I've ditched the budget vintage amps in favor of the Onkyo A-9555 integrated amp. It's about 85/170 wpc into 8/4 ohms, and has a seemingly non-existent noise floor. Very quiet, dynamic, nuanced for the price, and musical once it breaks in (takes about 100 hard hours).

You can get one from Amazon new w/warranty for around $474 with free shipping, or a factory-refreshed B-stock from http://www.accessories4less.com for $400.

I've lived with mine for 6 months after years of using an Amber 70 and a VSP Labs TransMOS, and this Onkyo trumps 'em both in pretty much every way. The VSP is 150 wpc, but the 85 wpc Onkyo sounds just as big. It delivers big current instantaneously.

Forte 1A...50 watts of pure, GLORIOUS class A power. I LOVE this amp. They are getting harder to find, but usually sell used for $400-$500.

You didn't mention what speakers you would be driving but the Sophia Baby is extremely sweet sounding if you can get by with its low watttage. Sell new for ~$800 but can be found used or demos for around $450 on Audigon.

Musical Fidelity A3CR is exceptional, versitile and an overachiever by far for the used cost. Might cost just a tad more, but you might pick one up for under $700.