I think all parts cost me around or less than $30-$35 from Lowes and Harbor Freight. Its just 2x3's cut to the dimensions you want depending on size of canoe/yak. My 15ft canoe is a bit wide for the dolly but it was a first try. My next will be slightly different. Likely wider than the first but it works. The pic's were taken just before the last cut was made. I still need to take pic's of it completed but Im going to paint it first and when I use it this weekend I'll take a bunch of pics of the canoe on it and all that. I just wanted to share how cheap and easy it was to make.
Parts include: 2 ten foot 2x3's (had about 8ft left over 
), a 3ft threaded rod for the axle, 2 nylon locknuts, 2 washers, 6ft small pvc conduit (have 4ft left over), 2 ten inch dolly wheels, and a box of 2 1/4" deck screws. Keep in mind this was built inside my apartment with minimal tools, cuts were made with a hacksaw and one was made with my drill Improvise, adapt and overcome 
To be continued... 
Alright, it rolls awesome on the concrete but as soon as I hit sand the top "T" portion or "bunks" gave way 
. needs to be cross braced or something to be more rigid. I modified it and should work now but haven't tested it yet. Will this weekend and I will post more pics then.