Check out nybrewsupply.com. They are inexpensive and are going to custom mine quite soon. I'm getting a 75 foot 3/8" chiller.
People will say that they are less efficient than copper which is true, but I am guessing it's not that different. The stainless tubing is not super heavy gauge/thick which negates the difference. Besides, you're supposed to be either whirlpooling or at least moving the chiller around in the kettle. If you do, there should be very little difference in performance, in my opinion. So, I just got mine longer to compensate. It's all about surface area. So, if it's performing well, then I see a benefit. SS is easier to keep clean and looks nicer. Also, if you get a tingly feeling 'down there' every time you buy stainless steel, this will work nicely for you.
Yeah, cooking with copper pans is freekin awesome, but it's not like I can't make a nice seer with stainless steel. (OK, the sandwich aluminum core stuff is better....I know)
Copper will chill your wort better, but it is a pain to keep clean. I have to remove the copper oxidation before every use. It's not a big deal, but if I have to replace my chiller I'd go with stainless steel. Actually, I'll probably go with a stainless steel plate chiller.