Ever so long ago when I was doing the craft show circuit, I had a friend suggest that when pricing an item to decide on a reasonable hourly wage, say $10 per hour. Keep track of how long it takes to make the item, say 60 minutes and double it. That would cover your time, talent and materials.
I am sure that if you were making them assembly line style you would take less time so,……I think the $10 - $12 dollar is not unreasonable but do charge more than $4.
This is Just a suggestion. You are getting lots of good direction form the board. Pick one and return to your machine and sew on!