Where I grew up is this huge private Christian community compound that has these tiny houses that people live in when they come once a year to plan the overthrow of America or whatever. While the church itself is big enough to park a plane in, the houses are wee like the ones in this video.
There are larger versions of this house that are pretty affordable if you get them used. They're called "mobile homes" or "trailers" and you may find those more economically viable, so long as you don't get one from FEMA.
"I really couldn't afford a large house with the kind of features I have in my small house"
Yeah, I guess ripping out all the real plumbing in a large house to put in your gravity-fed shower tube, among other "features" this small house has, would be pretty expensive.