As a suggestion though, why not just try checking online - currys,argos, BT shop, diy stores etc. I actually got a good deal from BT some months back - twin dect cordless with answer machine, text, and a sim card reader for about �50.00.
Just read your question again and am wondering - do they make cordless ansaphones? Cordless phones with an answerphone, yes, but stand alone ansaphones?