My recommendations would be to search yell.com or similar and contact you local joiner. He should be able to knock you on up at a fraction of the price of a shop, and especially the internet taking postage into consideration.

I would imagine it can get mighty chilly where you live, so a glass vivarium is a no as they don't hold the temps very well. Go for thick melamine wood.
Mine is 25mm thick, which is not a standard thickness, only joiners make them that thick, as it isn't financially feasible on a large scale.

My 4x2x2 ft (That's minimum size for a beardie by the way) was just £60.