I'm very partial to Icynene. I had an excellent experience with the product, and can't imagine recommending another manufacturer. This was the first winter since I used it in my home, and my utility company tells me my home was among most efficient in the area this winter - which is saying a lot for a house that's more than 100 years old!
There are significant qualitative differences between home manufacturers and foam installers, and done incorrectly, this process could have a very detrimental effect on your home. If I were you, I'd contact Icynene dealers in my area and let them compete for the job. Generally speaking, when you get a price from a dealer that's dramatically less than everyone else's, something is being left out, and it's foolish to go with the lowest bid. So get a sense of the average cost and ask questions of dealers from there. Good luck!