I do think that you have at least one viable option in that price range. I would suggest that you pick up an Adcom GFA-555II. It is 325w per side into the 3.5's 4 ohm load, and should power your Thiels quite well. Some folks don't care for Adcoms, but to my ears, their older bi-polar designs are really great amps for the money. Check out the archived reviews on Stereophile.com. Another advantage of the GFA-555II is that if you pick up a second one, you can run them each in bridged mono mode, putting out 850w into each Thiel. This is exactly the configuration that I use with my CS3.6's, and I find it to be quite satisfying.
Hope this helps, Tom.
Hope this helps, Tom.