What's not very expensive? If you give a budget then it might elicit more responses. Saying that most people on here (at least it seems that way to me anyway) are DIYers and will have built their own. Does it have to be a full sheet, can't it be a half sheet. Reason I'm sayng that is that it cuts the cost down enormously and brings it more into the realms of the average DIYer....I take it you're not looking to build one yourself, which would be the cheapest route?