I've spent about 15 today for wood and screws and built mining rigs out of wood, each able to hold 5 cards. Took me 30 minutes to build both.
I don't think you can get much cheaper than getting some wood and screws and building it yourself.
What the motherboard sitting on? Care to post a picture or 2?
Also, anyone using anti-static mats under the motherboard (for the metal and wood framed cases), not that you need one?
Thanks
Wood 1"x2" slabs area good choice for an open frame base because it's non-conductive and you can easily screw motherboard standoffs or a round plastic pen tube cut in to 1/4" sectons in to it.