Somewhere farther back on this list is a post about yurt living that I posted. It has photos. I think economically the poster with the RV idea is right on. The yurt or wall tent is a great option, but really, it's just your shell, then you need to install a kitchen, bathroom facilities, etc. By the time we were done with all that, and a water system and power system, we had spent around $50K. But living in a trailer would be tight with 2 kiddos. We have one child (2 yrs) and we appreciate the spaciousness of our yurt.
It's all about what works best for your family. It is a stress on everyone to be cramped up in a small space, but also stressful to spend a lot of money on a temporary housing situation. I think it's best to spend enough that you are comfortable if your house takes longer to build than you think (Cuz it WILL), but spend little enough that you don't significantly break into funds you could use for long term infrastructure.
Depending on your area, it might also be worth it to rent while you save and build. Sometimes I wish we had done this....
Amanda, DW to Drew, mom to Ella, 7, Gardner, 2, homesteading on the edge of the continent on the Lost Coast.
California Homesteading, http://eastmillcreek.blogspot.com