There is quite a market for them, don't knock it. Buy a cheap lot somewhere, pour a slab, wheel the tiny house into place, nice starter home for a young'un in one weekend flat.
Pour a slightly larger slab than you think you need, and call it a patio. Inevitably no matter how big a slab you pour you'll find a way to fill it up and wish you made a bigger one. The folks I know with RVs and hunter's cabins and similar want to spend time outdoors, that was the whole purpose of the purchase, and the tiny cabin or RV is just somewhere to sleep out of the rain, they actually live on the patio when not hiking / fishing / hunting / snowmobile / whatever.
I wouldn't bother with the slab either. Set it on blocks but also ensure that it's anchored on all 4 corners. Instead of a septic tank, change the design to incorporate a Clivus Multrum toilet and put in a large water tank for rainwater and to act as a heat sink for a heat exchanger. (Depending on climate, of course.)
Bonus if you live in the boonies and have to burn your trash.