airSUP are made at the same factory as red paddle, C4, RRD and a few others so the quality of the boards are very similar.
in Australia at the moment we do not sell through dealers so there is no middle man taking a cut - hence the price difference.
although best max weight for surfing is about 90Kg, it depends on the rider's experience...
one of our staff is about 107Kg, he rides a 9'6" airSUP
the more weight you put on it the lower it will ride in the water, so it will move slower. airSUP we have in Australia now are all 4" thick, so if you want to load up with yourself and a few kids then a 6" thick Naish might be better choice.