I may be making this up, but I believe I have seen (somewhere in my travels) an Esquif Prospecteur 15 set up from the factory as a solo. Not sure if they would draw in the sides a bit for you if so, but that would be a relatively inexpensive solo that cost 2/3 to 1/2 as much as a comparable composite boat.
I also like the idea of a Huron 15 for that role, which is a couple of inches shorter than the Prospecteur, but still taller than an Old Town Camper or Pathfinder, and in T-Formex Lite weighs less than 50 pounds. That is a very alluring boat IMHO...