Cob is definitely not fast, and is very permanent (centuries if it has a good foundation and roof.) If you want a cheap, fast temporary house that is well insulated, you might be able to build a wooden frame and roof, then stack bales under the roof and plaster them. If you don't take the careful steps to make it long-lasting, it would probably be fairly fast. It will be cheap only if you have straw harvesting close by, and maybe not then, depending on the market. For a temporary shelter, hay bales would probably work and be considerably cheaper.
The size of building you want (including wall height) will influence this advice. The bigger it is, the more important it will be to build well and add the strengthening touches.
Putting the camper inside a structure or shelter of some sort seems to have worked well for a number of people.
I've seen several people augment an RV with a tiny cabin at the front door, with a woodstove. Safer than cramming a woodstove inside the RV, and provides a nice mudroom/drying area, priceless in damp cold climates.
'Theoretically this level of creeping Orwellian dynamics should ramp up our awareness, but what happens instead is that each alert becomes less and less effective because we're incredibly stupid.' - Jerry Holkins
At the moment, I am thinking straw bale might be quicker to build since the straw bales in the walls are probably bigger than loafs of cobb. I'm basing my guess on that if this was all done by hand than bigger volumes of material (with a lighter density) would probably go up faster than smaller volumes of material for the same size house.
Would anyone out there have any experience in building a straw bale greenhouse? That I hope will be my project this summer. To build one in an existing barn. So work will be nice and dry. I’m dreaming of having my citrus trees leave the house and have their own house this winter. Dreaming of lemons in the snow.