Internet, Boating World.
you do not pay tax on the purchase but remeber that if you are going to register it then your state will collect the tax. (unless you live in Montana) The ones with inflatable floors are easier to store and set up but you are giving up some rigidity, standing stability and durability. You can get some clones on E-Bay at 2/3 price. Prefer an inflatable to a rigid for stability and weight carrying capacity.