The cheapest way to start from scratch is still buying the plastic pond or Rubbermaid trough (at least according to the prices on the Tractor Supply website); the 8'x 2' circular plastic stock tank is the same price as the 8' x 2' circular galvanized metal stock tank according to the local prices for my nearest store.
I would agree but I found a galvenized 450g stock tank for much cheaper than I could get a 300g plastic stock tank.