Where to get a cheap greenhouse

Ok so im trying to get alittle outdoor hydroponics going and i wanted to build a constant lettuce(maybe) grow in a greenhouse. I have some tomatoes im going to build a gutter ebb-n-flow with but for the lettuce i dont wanna have to worry about rain changing my ph(the tomato stems i can more easily cover up so no water gets in). Ive been shopping around looking at the dome style plastic covered setups but they all seem to be overpriced. One guy on a pepper talk forum here said he got one like 6'x10'x7' for around 200$ after shipping and was wondering if any have seen a similar setup or know of a way i can do this without blowing my wallet out hehe. Any info would be greatly appreciated. Keep up the good grows =)

PVC Hoophouse cover with plastic

http://westsidegardener.com/howto/hoophouse.html

http://doorgarden.com/10/50-dollar-hoop-house-green-house

Man thats perfect, even more then i expected per 1$ +++reps

if you want an even smaller one than that you could do like ive done. You get a plastic 4-5 shelving unit(around $20). Take two or three wire coat hangers and make hoops ot of them and then duct tape them to the top to make the frame of the top. then cover the front and the two sides with clear plastic and secure with duct tape. Cut a piece of black plastic the size of the back and secure it at every shelf level with velcro pads. This way the clear plastic allows the light to enter and it is absorbed by the plants, soil, and black plastic and creates heat in side. I live up in the frozen north. When the thermometer outside reads 20 the thermometer in the greenhouse reads about 75.

It should kinda look like this

btw if it gets really cold out you can always just pick it up and bring it inside