I would just steer away from the closed cell foam in your situation.
All of a sudden there is a rush for foam, like the energy crisis in the 1970'S on plain old fiberglass.
Try another route. Go to Nu-Wool :: Premium Cellulose Insulation :: Home Page
. I recently talked to a group from the Building Performance Institute on these subjects.
You can get the same results from the blown in insulation at much less of a cost. I do not work for these folks or anything else, I just respect their product. I was skeptical at first, them I went over the results from the independent study.
Let them come out and actually tell you what they are capable of.
Besides that it is green, Energy star rated and you may get some tax reductions for it's installation. And half the cost.
There are no spray foams available for DIY, unless you start your own company so you can buy the chemicals.