I've made my own with my explorer group. we used ripstop nylon from an online shop selling supplies for people who build kites, and paracord for whippings, and used nylon webbing strap for tree huggers. we where using blue polypropalene rope for mainlines, although I later (and at extra cost) changed to climbers accesory cord.
I think the total cost was about £10 maybe a little more, although we where buying in stuff in bulk, (100m roll of paracord can happily do ten hammocks whippings with cord left over for example) and stuff like P&P costs would have been spread out.
I love my hammock