Here is something that probably falls more in the "crafty" category, but I did save money with it since I didn't have to buy any ... footies!
I made my son this pair of footies in probably about an hour this evening. I used some yarn I got from my mom and single crotched it. I'm going to make him another pair just like it so he'll have four shoes to wear.
We made these all the time for ourselves and each other. You just knit or crochet a square and then sew it up with a crochet hook. Simple, cheap, and so warm and cozy!