Here we go...

I have put together a home built set that are not quite as good as some of the more expensive types I have seen but for 100$ they still work amazingly well. The design is different with two separated strap on wheel sets so I can single handedly pull the boat of the trailer with the wheels preattached. The wheels arn't as big as most cat haulers but there is 4 wheels instead of two giving enough weight dispersal for moderatly soft sand.
I haven't had a chance to test them in very soft sand yet. The Wheels are 10$ each with bearings from Super Cheap. The Axles 40$ from a steel Company.. The Hull Shaped supports cut out from a large White Bucket 17.50$ from Bunnings which is then coated with a 5$ rubber carpet from Para Rubber. The axle passes through a aluminium square tube 10$ which the bucket mouldings rivit onto... 2 adjustable straps with clip in buckles 10$ A few Split pins and washers to position the components on the axle 5$..
Because the axles are only 2 feet long they are light weight and fit happily inside your sail bin.

By strapping the wheels to the end of the hulls you can easily wheel the boat off the trailer single handedly. Then shift the wheels further up the hulls to take more load.