Lastborn,

Welcome to the fire, newguy! $30-50 is a pretty low price. What sort of stuff do you want to filter? Just biologicals (bacteria/virii) or also chemicals? Will this filter be responsible for supplying all your family's daily needs or just for the occasional use backpacking?

Without further information I'm going to assume you want biological and chemicals removed for daily family water needs. For that your best bet pprobably would be a sand filter system. There's lots of plans for these on the web and even a few discussions here on ETS.

-Blast