FR-4 is used almost exclusively, and is very inexpensive. Check with any of the board fab houses. A couple advertise on RF Cafe (no, I'm not one of them). From a quick look here are the ones I see (might as well support them since they essentially pay for this website). Sorry if I missed a couple. I think they all specialize in quick turn-around and even small quantities.
American Standard Circuitshttp://www.asc-i.com/
Johnny G. in beautiful Wisconsin