Foam panels are going to bit less expensive because you don't have to rent the maching or hire a Pro to do the spraying. However, the spray-in insulates far better because it completely fills the cavities. Plus the spray-in fills gaps that allow drafts. In effect it seals the space.
My garage is insulated with 3 1/2" OC "Pink" fiberglass batts that were installed when I built it. That gives me a value of R-13. I also added Tyvek wrap around the whole house and garage to reduce air infiltration (drafts).
Back to the garage door question... I was just browsing and found this link:
http://insulation.owenscorning.com/h...|S||4769474429
On this page is a button to download a PDF about OC's Garage Door Insulation Kit.