[Joni]

The difference in price is simple. It will start with PVC/Vinyl bladders or Urethane. Difference? The first stretches, which means effected by altitude and temp changes, won't last as long, heavier, and doesn't support as much weight.
Urethane on the other hand does NOT stretch, is not AS effected by temp and altitude changes, LIGHT! and last a very long time. Urethane will however cost twice as much.
It has to do with how the bladders are made also.
NFO (Scadden) boats are now BLADDERLESS and not effected bu the eliments, PLUS look at the pay load they can handle.
Bucks Bags and NFO and """ONLY!""" the Outcast PAC 1100 and larger (can tell by the price) are all made in the good old USA. (You might want to consider that when you think part of the reason our gas prices are going up so high, is because we are bidding against China). All other Pontoons WILL be PVC bladders and probably from China.
Valves make up a very big part of it also. Halkey Roberts are the best in my opinion.
It has been mention already that a Tube/U-Tube or even a V-Tube are not a good idea for rivers because of the dangling feet thing.
The NFO Freestyle H3 is on exception due to the fact it is 6' long and you can lift your feet up. You can even control it with Kayak paddles.

Please get something trust worthy. Think of it as would you jump from a plane with a parachute bought at a thrift store?