After 4 pairs of pants piled up of my recycle or mend pile, I finally decided to give it shot. First step, acquire iron-on patches. You can find these fairly easily at craft or department stores. I got a multi-pack at Target: with 8 patches of varying colors of denim and khaki that can be cut to size, it's only pennies per patch.
Trim the patch to cover the holes, and iron on. Follow the directions on the package: mine was high-heat, no steam.
You could stop there, but iron-on stick tends to wear off after a couple washes. We can easily reinforce the patch by sewing back on forth over the edges.
Minimally noticeable from the outside - at least, less noticeable than skin showing through. ;)
(Image from womanwithwingsblog.blogspot.com)
(Image from honestlywtf.com)
After an hour of work, I repaired 4 pairs of pants. Here's hoping I can now double the life of the pants, saving my self potentially $100s per year.