I did my dual 4-gallon setup for under $20. Used pots from store-bought plants as net pots, used sterilized cat litter sand boxes for buckets (Thank you Fresh Step,) the only things I really paid for was the hydroton, the air line, the air pump, and air stone.

DIY ROX! Good job on your setup, man! I'm going to make a 4 plant 4-gallon DWC for herbs.

Also - http://vimeo.com/3729005 - There's the construction demo vid
http://vimeo.com/3910153 - Sweet basil, day 1 after transplant
http://vimeo.com/4032897 - Same sweet basil as of today, one week later.

I'm going to move everything I can over to DWC, even outdoor stuff.