There are a number of ways to get it done. This one for example is under 3000
The Pinup house featured cost $3,000 in materials to build. It is basically a 10' X 10' structure with no plumbing, no heat and no electricity. You mentioned you were spending the bulk of your money on the land for your Pinup house which means land must cost more than $2,500. Using your figures, my math suggests that your math is somewhat off. Anyway, where can you buy land for $2,600 dollars? I assume you do not plan on getting any building permits because building permits alone might eat up most of what you've set a side for materials.
Look, I really wish you the best, but you are not being realistic about this project.