Pinoikoi, that depends-- a sledgehammer doesn't cost much
as long as you're not knocking out supporting walls, you can do all that wall work you described for very little cash and a big mess to clean up
even trimming out the walls isn't that bad (this from a farm wife homeschool momma who is very, very seriously broke!). the bathroom redo could get costly, but you could do the other stuff and postpone the bath part, if you were really feelin' the call
momofmine, what about something temporary, like a cabin tent in the yard? or what about enlisting a friend to help you do a tremendous purge, then see how much stuff you have? what about more clever storage solutions, dual-purpose furnishings, going vertical with stuff? in other words, how far towards the space you want can you go without having to build more space? imho, better to reduce needs to the minimum before expanding unnecessarily, kwim?
I can't remember if it was this thread or the purge one, but someone recently posted a video of this guy's apartment... darnit, I can't remember the details. I *think* it was in tokyo but I'm not sure. anyway, it was super tiny, about 350 sq ft, but he had built these amazing rolling walls so rooms essentially collapsed away when not in use. I'm thinking of getting dh to build a double-sided bookshelf wall on wheels modeled after that idea. if it's done right so the shelves are adjustable, it can hold all kinds of things which can change as the kids' needs change, including lots of homeschool supplies, toys, collectibles, and obviously books. thinking of your boys possibly wanting a little more privacy, I wonder if something similar could work in your house? a rolling wall that might close off an area in a room where there's a tv or game console, for instance, where they could hang with their friends with a little extra privacy? have they asked for this privacy? maybe they have ideas about how it can work in the space you already have.
just brewing ideas along with my decaf