Two possible budget-saving alternatives have been done in my neighborhood in the past year:
1) Build a second, winterized, floor on top of the existing structure. (This was done to a 60-year-old cottage with a marginal concrete-block basement).
2)
Lift the entire existing structure, and put a poured concrete basement
under it. (Only $50K—and also a 60-year-old existing cottage—I may have this done to my cottage).
Both turned out beautifully. If no additional bathrooms are added, the existing septic may get OK'd.
Also, new construction may limit the number of seasons that you can use it
while it's under construction. For example, a "new" house next door is still not finished, and next season will be its fourth year "under construction".
