I saw those clarkes rubber ones too and had the same thought - I want to find that sort of thing but with a vinyl/pvc cover insted of one that you take off and wash. We had a wipe down change mat for DS, and I think that probably alot easier than having to wash a cover of you get a poo explosion or similar.
I wouldnt want to be paying more than up to $50 I think.
I havent started looking properly yet, are they hard to come by in the wipe down covering?