Amp to drive my AR-90s

I've heard differing opinions on how many watts per channel I need. What do you suggest to drive my 4-ohm AR-90s?

If I want to stay under/around $500. What used models should I be looking at?
Are you looking for a basic amp or integrated? As for power as much as you can get , especially if you like to listen at higher volume.
Just something to run my Rega TT...not at super loud levels. I have a couple 5W tube guitar amps and those are pretty loud when cranked...don't know how that translates to an amp driving some AR-90s.

I'm not sure what the difference between integrated or basic is. I just need an amplifier, I don't need AM/FM or a bunch of channels or anything.
I've got a pair of AR90's. I'm driving them with a Harman Kardon HK3490 receiver (120w:89ohms/150w:4ohms). If your source is a turntable, the 3490 is definitely enough power. It's around $400 new price. Mine is B stock which I bought from the factory on ebay where they are auctioned off for $229. There was a reserve at the time--they didn't call it a reserve, but you couldn't get it for less than that. The sound is really nice with the 90's. I like it a lot.
As much good clean power as you can afford ..... They are very inefficient and like a lot of power to sound their best .... The power really opens them up and is not just for volume ...
I am looking at picking up a used Adcom GFA-555 once I get my speakers fixed. 300 wpc into 4 ohms from what I've read...
I ended up with a GFA-555mkII and a GFP-750 preamp. I've got all the speakers refoamed but one of the 8" is rubbing.

I'm thinking the spider might be gone on that one...look for a replacement now.