Cut & cobbler before spray foamers to save on some board feet – GreenBuildingAdvisor

So I ripped a late 1800’s early 1900’s house to the studs in Massachusetts climate zone 5. Doing a full gut and remodel and finishing the attic space as livable space, there is about a 3’ crawl space above the livable area now . My plan was to spray foam the entire envelope closed cell in the walls and roof but I simply cannot afford it. I could how ever afford open cell in the in walls and floor joists of the basement and closed cell on the cathedral part of the roof and over spray open cell in the crawl space. 2×4 wall framing and 2×6 roof rafters. Getting me a r15 in the walls and r38 on the roof. However I can get my hands on cheap 2” foam board from $5-$10 a 4×8 board so I was thinking I could cut and cobbler the entire house and spray about 1-1.5” of cc on the walls and the roof will stay the same to save some money or for the same money as open cell end up with a better performing end product. If staying with open cell I could significantly save some money putting rockwool in my self in at least the walls and spraying just the roof