el. 

I bought a hoop bender from Johnny's Selected Seeds and made my hoops.  Then I put the hoops on the rebar and covered the re-bar with greenhouse plastic.  I rolled the plastic around a piece of wood and secured it to the ground with heavy sandbags.

Finally, I purchased a zipper that sticks to the plastic and was able to create a door to the tunnel.

The cost of the high tunnel is dependent on the number of hoops you use.  In other words, its by length.  A roll of greenhouse plastic will run about 100-130 dollars and the other materials are about 7 dollars per hoop.  I placed my hoops just 30" apart.