Hypalon can be wonderful stuff, but you shouldn't be paying anywhere near $6000 for enough to skin a yak.

Some things to keep in mind if considering Hypalon:

Hypalon is the DuPont trade name for Chlorosulfinated Polyethylene (CSPE) which is chemically similar to the more common PVC.

Hypalon is a "thermoplastic" sheet made by calendarizing (sp!) two thinner sheets over a reinforcement of woven polyester (usually). Without the polyester reinforcement it would be somewhat elastic (I'm not sure if you can commercially obtain unreinforced sheets, although they might have an advantage when trying to conform to compound curves). Thermoplastic means that the material will plasticize (melt) when heated. This is how two sheets are permanently bonded together. Over time (generally less than 1 year) Hypalon will thermoset, meaning that it looses its thermoplastic properties, i.e. it can no longer be patched with like material. UV rays accelerate the thermosetting process. Once thermoset, Hypalon can only be repaired with adhesives, which produce and inferior bond as compared to heat "welding".

Hypalon is readily available from your local roofing supply center. However, generally they will only sell full rolls. However, if you patiently explain that you need only as small amount, they might give you the names of some local roofers that install the material, and you could try buying scrap from them. A 4' x 80' (the smallest available) full roll of .050" thick "UltraGuard" brand Hypalon roof membrane will cost you $294 at my local roofing supply center.

You might be better off considering a PVC roofing membrane. PVC membranes are produced in much the same manner and have basically the same good properties as Hypalon, but they won't thermoset, so they can be patched (by heat "welding") whenever required. I would go as thin as possible (.048" or 48 "mils" thick) to cut down on the weight. It should also be readily available at your local roofing supply center. PVC is also superior to Hypalon for submerged applications because it generally will only gain 3% or less water weight through absorption (Hypalon is higher, but not by too much). Warning; if you go to your local roofing supply center and ask for a PVC membrane, they will frequently sell you a Hypalon membrane because they do not differentiate between CSPE and PVC, be sure to verify. Sarnafill brand (I wouldn’t buy any other) PVC roofing membrane in .048” thickness will run you approximately $400 for a 6.5’ x 65’ roll. It weighs 0.32 pounds per square foot.

With either product (PVC or Hypalon), care should be taken to not expose the reinforcement at the heat welded seams. The reinforcement will "wick" water into the sheet, reducing it's life expectancy and increasing the weight of your boat. Heat welding is tricky and requires some specialized equipment, namely a hot air gun (hair dryers don't even come close, but somebody make an attachment for propane tanks that is designed for the job). Hot air guns are obscenely expensive, but you might be able to rent one somewhere. Solvent welding of seams is possible but far inferior to hot air welding.

Sorry for the dissertation.

Porter in Maryland