Tube amps

While the WP's are nominally efficient and marketed as being tube amp-friendly, they require an amp that can produce a lot of current to control the woofers (the impedence on WP's drops very low in the bass), which rules out the vast majority of tube amps if proper bass performance is important to you.

The CAT stereo amp will definitely work (it has monstrous output transformers and can drive 2 Ohm loads). Even at used prices, however, it exceeds your budget. If you have to do it on the cheap, maybe (MAYBE) the Sonic Frontiers Power 2 will work (Power 3 monoblocks would be better), but I have not personally heard that amp on Wilsons.

The safer bet, due to the WP's current requirements, is a really fine solid-state amp. The Rowland Model 2 has a pleasing midrange, very high transparency and great build quality, and assuming the rest of your system is up to the task, sounds particularly good if used with the optional battery power supply and run balanced.

While many tube amps can make sound come out of WP's, few can control its woofers properly -- you need to be very careful pairing a tube amp with those speakers.

It was my understanding that tube amps are better at handling low impedance loads - am I wrong?

It's the speakers which lack the warmth

I agree with the other posters above. I have WP7's and while they are voltage efficient at 92 db/watt, they are a difficult load in the bass. I tried some 15 wpc SET Cary Audio amps and the bass was flaccid and the dynamic range was compressed. Nice on voices and acoustic instruments but poor in bandwidth and dynamics. I then powered them on Conrad-Johnson Premier 140 and Audio Research VT100 Mark III tube amps, which are quite neutral tonally and sounded terrific on the WP's. Yes, they gave up some of the bass impact and dynamics of the best SS amp I have heard with them, an Essence Emerald II, but there is no beating tubes for warmth and dimensionality. I thought the C-J and ARC amps to be the best middle ground between typically dry and flat SS, and warm and dimensional tubes. Of the amps you list above, my gut feel says the Cary amp because of its multiple output tubes and probably lower output impedance, but I really think your best bet is one of the larger push-pull tube amps or a really good, powerful SS amp. The dynamics and bass of my Essence 250 wpc SS amp must be heard to be believed. The trick, as always with SS, is finding one that has some of the dimensionality and warmth of tubes. There are getting to be more of these recently, so maybe a good SS amp from C-J, Pass Labs, Jeff Rowland, or even a used Essence amp might be the trick.

Tube amps are usually not as good at handling low impedance speaker loads due to their high output impedances. A typical tube amp output impedance is about 0.5 to several ohms, while solid-state amps can have impedances down to 0.01 ohm, depending on many factors including global negative feedback. Because of this, SS amps usually have more control in the bass frequencies.