Any plastics shop or storage container shop carries great acrylic cubes. I just got a bunch of 4x4x4 cubes that I'm modifying to suit my needs.
If you need something bigger you can buy and modify display cases designed to display footballs or basketballs.
In my opinion tarantulacages.com is way too expensive if you're willing to put in the labor yourself. With a little bit of practice and about 40-60 dollars worth of tools and about 20 dollars worth of material you can start making all the enclosures you can shake a stick at.
Some links on places that carry fairly priced acrylic display boxes:
http://www.containerstore.com/brows...=14231065&itemIndex=97&CATID=233&PRODID=62553
http://www.tapplastics.com/shop/product.php?pid=222&
Those are the cheapest sources for the two styles of display boxes I use for my slings and small juvies. I use the boxes from the first link for avics and the ones from the bottom link for everything else.
Just search around if you need something bigger, both suppliers have larger boxes if you look.
The Container Store is *slightly* cheaper but TAP Plastics will also sell you an acrylic drill bit which you *need* if you want to make professional quality holes (or any holes that aren't a melty mess and aren't cracked and chipped, at least).
I think tarantulacages.com's cages are worth the price if you want a nice uniform set-up. Beleive me the practice alone is gonna cost you if you want a nice clean lookin cage. And where can i get material to build a nice good size cage for under 20 bux?