Graphic Design pricing question

Hello, I was wondering if anyone could give me some advice? I'm a Graphic Designer and someone contacted me about using an illustration I did for their Tattoo. They want me to do a full color version for them. This is outside of my experience I was wondering what something like this goes for? Any advice is appreciated.

Hey I am a designer as well and in that case I take it from where it comes from. If its a friend and the piece will take me an hour to draw, I may be do it for free or give them a good discound. If its some random person and they come to me for a design inquiry then I just bill them based on my hourly rate "$150" Fallen King Irons - http://fkirons.com

I would come up with an hourly rate that you think is fair. Do you have a portfolio online somewhere?

Thanks for the replies, I was going to just charge him my hourly rate ( he's just a random guy who likes my work) But I just wanted to make sure I wasn't making some Tattoo faux paux . Thanks