Also, if you want close to passive house, you'll need way more than R-21. I would say only use spray foam if your wall cavity is limited and you need the maximum R value.
Spray Foam although rated at R-21 preforms much higher since it seals. Blown in Cellulose settles, attracts dust, rodent nesting, and doesn't seal and isn't a vapor barrier or water proof. You get what you pay for I guess.
We have a house in Northern Ontario that is around 4000 Sq/Ft (entirely spray foamed). The costs to heat and cool it are 1/3 compared to the house 2800 sq/ft house in Toronto (insulated with Fiber Glass, Attic Cellulose).
The biggest hurdle is folks just don't give a fuck about the mechanical part of the house. Dry wall covers it all up. What's important is the finish that you see everyday.