Here is how I built one of my bongs.
I went to the flee market and picked up 1 stem, 1 bowl, and enough rubber seals for the design( I needed 2 most bongs need 1). All this will run you $2-$3. Then take a plastic container that you can suck out of and put a hole in it a few inches from the bottom. Make the hole just big enough for the stem with rubber seal. Put the stem and seal inm the hole and smoke away.
Bongs are super east to build.


Here is the some pics:
http://boards.cannabis.com/showthread.php?t=9182