Prefab and you don’t want to do much work? Target might have something for you. Actually, it looks like the work (done by Christopher C Deam) might just be a “modern trailer park“. Somehow I think a wall of glass is going to sell less well in an actual trailer park, vs. someone who bought an acre of land out in the boonies.
Ready Made Mag had Edgar Blazona (of modular dwellings fame) make them a back yard shack for $1500. They have full plans in their store. This is structure is designed to be a low cost extra room for the backyard. As a result there is of course no plumbing, electrical, or insulation. The structure would make a fantastic office, studio, or guest house. If you need full amenities, he has also designed a nifty granny flat named the MD280.
Usually in prefab, massive chunks are constructed at the factory and assembled at the build site. Master fit takes a different approach. Smaller pieces, everything is numbered, everything fits. The goal is to allow unskilled people to be able to easily put up a frame. The materials are more expensive than usual, but you will save on labor. The frame also ends up being stronger because of the fit.
If you really want to get involved in building your own house, you can go the straw bale route. Here is a site of a guy building one in Baja, and here is a site for a woman who built one in San Diego county (Ramona). The one in SD was featured on the Green Built tour. Reading through the sites you will notice some very different building experiences between them. In the US there is a lot more red tape and bureaucracy. As an example, in SD they won’t let you use straw as load bearing walls (despite their strength and earthquake resistant nature). Instead, you have to put in posts and beams for the roof.