I searched out there for boat dollies and found none exactly meeting my requirements. I wanted something sturdy, compact and affordable. To me affordable is UNDER $100. So I made my own.
The sturdy part I satisfied with paint-lock steel sheet, rugged wheels used on large garbage barrels, and non-skid rubber decking.
The design is compact enough to allow me to put the boat dolly inside my sea kayak's aft storage compartment. And it's light enough not to be a burden.
Affordability was met by making a unit that could sell just under $100 retail.