As of just a couple of years ago you could buy the basic kit, including shipping to Bluefields, for about $2500: one bedroom, living room, kitchen, and bath. The kit prices may have gone up since I asked, but they're probably still eminently affordable.
Also unfinished is this house. I don’t know how many bedrooms or baths this one has but it's got a nice layout. In this house it's easy to see how the finish coat covers all the seams, just the way a finish coat would cover seams in a house built entirely of block.