I purchased them from a designer in Maine called Shoestring Shipyard (
www.shoestringshipyard.com). As a caveat, I found the owner to be quite rude and condescending. The plans were missing several important pieces of data including dimensions, wood stock required for the build but missing in the bill of materials, etc. I would not do business with him again. My dinghy has come out great so far but I had to figure out quite a bit due to the poor plans.
I have worked with another boat plan company in the past called Bateau.
www.beateau.com They provided excellent customer service and support and the plans were complete. (I tried Shoestring this time around because I was referred to them as a provider of plans for the 'glue and screw' method of building - I had previously built boats via 'stitch and glue' plans and I wanted to try a new method).
The materials (Okuma, S2S fir, SS screws, West System epoxy, etc.) cost about $650. You could do it for less if you purchased regular AC exterior ply from Home Depot but this wood has voids, does not use waterproof glue, etc. Okume is the best you can buy, has virtually no voids, waterproof glue used in construction, Lloyds certified, etc.
It's very satisfying to know you built the buggy keeping you dry and safe returning to shore.