How much should i charge to do eye makeup?

I've done makeup for a lot of my girlfriends and their friends for free and i did makeup for a fashion show last month. Alot of the models were interested in me doing more work for them for upcoming parties and prom. I think i should start charging but i don't know how much? Right now i just do eye makeup. I can do anything from simple to extravagant. I use a variation of makeup brands from coastal scents to drug store to MAC and urban decay. When i have the money i will start doing full face.