The suggestion about welded wire is a good, probably one of the cheapest ways to fence. The dogpark uses split wood beams & chicken wire. We've thought about doing that to enclose a really big area, maybe 1/2 acre...someday.

We fenced off a large area by putting sections of fencing between our out-buildings. We used pre-built fencing sections that are nice because we can move them really easily....so of course, they are pretty expensive, too.