Messalina, do what i done, just get yourself a bog standard tray or any old plastic tray, drill some holes inthe bottom for drainage, go to a builders yard or garden center and buy a bag of very fine gravel, the sort they use to cover soil on pot plants tip some in, and your cat will be scratting away in it in no time the poo you will have to remove but then you can just swill the gravel now and again with the hose hence the drainage holes, you won't have to change the gravel for a long time, and don't forget you got a big bag anyway, a lot cheaper than cat litter.