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.
