These things are cool. They will build you one for less than 70k. You provide the trees.
- Build the Ultimate Tree House (spoonful.com)
- 12 Totally Amazing Treehouse Designs (redtri.com)
- World’s biggest tree house (bigpondnews.com)
- A Tree House ‘Coccoon’ For Backyard Camping (And Napping) (earthtechling.com)