For my mom's birthday I insulated her 16' wide garage door for just $150 and 3.5 hours. It took:

3x 4'x'8'x1" foilbacked Styrofoam panel
3x 25'x16" bubble foil rolls
2x 150' foil tape rolls

Between the bubble foil (R3) and the Styrofoam panel (R3.9) the garage door should be insulated to an R value of 6.9.

This was a quick, easy project and hope this video helps you do your own garage door!