I have the Lowes brand CT-101 that paid $90 for and I do not have a C wire. I read the response may be a tad slower (I have not noticed) and you will have to replace batteries more often but other than that its been working fine.
I also read you can rig up an AC adapter that when plugged in will work as the C wire, I am eventually going to try this.
Hope this helps,
Scott