How much should I pay for a 2001 Thiel CS 3.6?

Forget 4 Ohms, how about 2.3 Ohms!

Even 250 watts as a stand alone spec won't necessarily provide what is needed to power these properly. Trust me, I own them and love the sound of them, but it took a Krell 400 cx (even a 300 cx wouldn't do, I tried!) to finally get them to "light up" and pump clear, textural bass as they were designed to. Also, you need current to get them to warm up and sound sweet and delicate when called to do so. When you get the power right though, they are wonderful speakers.

An amp that doesn't flinch into 2+ Ohm territory is de rigeur.

I've had my 3.6's for over 14 years and have been driving them with a McCormack DNA 1 Deluxe that I had upgraded by SMc Audio to Revision A Gold with some extras in 1998. The amps are rated at 185 watts. I have to say that I have enjoyed them very much and I do wonder what they would sound like with a more powerful amp in consideration from the comments here. I do find them to be somewhat bright at times. I have been strongly considering changing the amp and letting the Thiels go in favor of the Vandersteen 5A's. Not sure when that will happen.
It is true that the tweeters are not in stock, however mine had to be replaced recently and I was able to send it back to Thiel and they rebuilt it. Good as new and they were a pleasure to work with.