We built this for less then $200, the hoops are PVC pipe, we had the plastic already, then we used utility polls sunk into the ground a couple feet. The sides are made of pallets from the Kubota Tractor dealer, the gray/white tarp is from the COOP, it was used to cover a huge pile of wheat all winter. We used the tarp to cover the pallets so the dirt isn't against the wood to help prevent rot.
If you do use PVC pipe for a greenhouse, be sure the pipe is covered because the PVC messes with the greenhouse plastic and it makes it age really fast, the plastic will get very brittle and fall apart.
Here is a picture of the greenhouse before we had it finished, you can see how it was built a little better.
So far the greenhouse is still standing, tonight it was 55 outside and it was 72 with 60% humidity in the greenhouse and that was when the sun was setting.
Edited by BTS, April 10, 2014 - 10:18 PM.