If you want a well built and efficient home (barndo on a budget) a barndominium or post frame (pole barn) home might be a good option for you.

With no basement, post frame homes have no in-ground foundation. The walls and framing are typically cheaper compared to a normal construction home.

Another, almost as efficient, option is to install replacement double-pane sash kits in your existing window frames. These are basically new replacement windows without a new frame.