Buy one. It's worth it just for the safety factor. You'll be surprised how often you'll or your buddies will use it.
I've gotten away with using hose clamps and motorcycle tie downs, Craftsman wood clamps, C-clamps and chain, a port-a-power with a dog lead ....
It's not a whole lot of pressure, you can just do it by hand, but have a friend around to line everything up.