Many years ago, when I was a poor man, out of despiration, I invented my own succah design. It has worked well for me, so I thought I would share it here.
My old succah was 10′ x 20′, eight feet high, and was very sturdy, easy to assemble (30 minutes for one person), stores very small, and cheap (about $250)!
The secret was to use easily available parts, which basically involved taking what the world calls a “Shade Tent” and retrofitting it.
There are basically three parts:
1) The frame.
2) The walls.
3) The schach.
For the frame, there are two parts, pipes and connectors.
For the pipe, I used 3/4″ x 10′ Electric Metallic Tube (EMT) Conduit, which comes in 10′ lengths at Home Depot for about $4 each. 
Assuming you are making a succah 10 x 20, you will need a total of 19 poles, 6 for the floor, 7 for the ceiling, and 6 for the vertical rise (which connects the floor and the ceiling). While you are at Home Depot, have them cut the 6 for the verticle rise to 8′ lengths, since you don’t want your succah too high.
For the connectors, do a search for Canopy Shade Fittings or Connectors. They will look like this and run about $6 each. 
You want shape C1 for your corners, C2 for your ceiling in the middle, and C4 for your floor in the middle. Total connectors are 8 C1, 2 C2, and 2 C4. For a total of 12 connectors. If you want to use the connectors, I used, check out this seller, but there are a lot of other places if you want to shop around.
By putting the conduit together with the connectors you have your frame! (Hint: For ease of assembly, remove the screw pins that come with them and put in screws that you can use with a cordless drill. If you buy from the guy I mentioned, ask him if he can do this for you before he ships.)
2) The walls are very simple. Just tarps, which we affix to the frame with ball bungies. Each tarp should be 8′ x 10′ and you will need 4 tarps assuming you leave one full wall open. Make sure the tarp says that it has grommits every 18″ since that is what you will use to attach the tarp to the frame. I like white walls, which look nice and suggest matching white 6″ ball bungies since they will be the easiest to work with. Each tarp takes about 25 bungies, so get a package with 100. Here are some pictures of what you are buying.
At this point, the total cost of the basic succah is $85 poles, $75 connectors, $40 tarps, $25 bungies, for a total of $225 for the basic 10′ x 20′ succah.
All you have left is schach.
3) I used wood to support schach mats, but if you really want to stay cheap you could just use real schach. To build the wood underframe frame, I purchased 8′ x 1″ wood sticks, and laid them in a herringbone pattern on top of the metal frame, which can then support your mat or branches. To be honest, it would be easier to buy some just over 10′ (by 3/4″) wood boards (less than 3 tefachim wide), and just use those, but I didn’t want to make an extra stop. In the long run, if you have a lumber supply house, I would go that route (and will do that myself for my new succah).
That’s about it, so have fun building and feel free to be in touch with any questions!