Regarding economics, it is 100% certain building a dug out basement with conventional floor system atop it is going to cost some real money. If you were thinking round foundation, well they are extremely rare. In fact I've never seen one.
If you go the rectangular basement route, and place a round yurt atop it, then you have to have an even MORE expensive membrane deck to protect the basement. Membrane decks are pricey.
If you build a root cellar within the footprint of the yurt, you'll need to leave the stair access area clear of belongings.
Frankly if I was considering a small home, as your husband might be thinking, I'd build a conventional two bedroom 28x32 rectangular rancher on top of a full basement. We have good friends that did exactly that and ended up with four children in that home.
Do some of the work yourselves, and finish the basement as funds allow. You could consider the unfinished basement the root cellar.
For real economy and to get on with things, a simple yurt on a wood deck- go with that. Don't worry. You could later pour a 12x16 slab on grade and build a shed with loft on it for a long term low maintenace dwelling that won't leak or fail in the worst storm.