[crosseyedsheep]

Here's a link to a a homemade poly tunnell, it looks pretty good, I think it would help a lot if you could get a proper steel support for each end, I'm not sure if you would save a lot as you're only substituting the frame with an alternative, you'd still have to buy the same cover, it would be interesting to do a price comparison:

Homemade polytunnel

[galwaybeginner]

Impressive site. Lots of detail.

[MrDamon]

I think this is the very same design that I worked from when I built my first tunnel.

Worked out pretty well and survived a couple of fairly harsh storms also.