It doesn't sound cheap. What is the climate? How is the roof vented? Is there a radiant barrier under the sheathing? The foam may have to be protected with 1/2" drywall. Did you do a computer analysis of the house?

Consider the Spider system of blown fg that can easily hit the R49.

You need a minimum clear airspace of 1" between the top of the insulation and the bottom of the roof deck. Depending on how far along you are, you could build an unvented attic, which works in all climates.

Thanks, I never heard of the spider system. I will do more reading. It seams that I would not have to use foamboard on the ceiling if I use this. The baffles provide 1.5" of airspace. The room is 23X22 with only 1.5 /12 pitch in the back and 10/12 in the front. This is a saltbox so the flatter roof span is 12'. As a result of the front 10 / 12 pitch the room is only about 23 X 16 usable space. There is a Cobra ridge vent and soffit vents so I hope this provides enough air flow. I thought about an unvented attic but was nervous. We live in upstate New York. For insulation purposes we would be in zone 6. Our spray foam estimate was over $5000 for this room.

Thanks again