I've tried some gravity bongs that are better then $100 dollar bongs....so go for it. Atleast they got me a lot higher.
Although they're not glamorous, homemade gravity bongs really do kick ass. Even standard bongs made from bottles are pretty decent if they're made well.
Everytime I try to make a water bottle bong it sucks. What should I use for a good stem and bowl or where I can buy one?