Request advice

Dear Everyone,

I thought this would be a good place to post and ask for advice concerning art commissions and prices. No, I'm not looking to hire anyone, but rather, inquire as to what people charge (if any of you do regularly paid work).

You see, lately, I've been having an increasing amount of requests for commission work, with people asking me what I charge and all, and I don't have answers for them. I got into digital art for fun and to make character images for my friends and I. I never charge my friends for work, but then I don't make one for everyone who asks.

Strangers and people not so close to me are a different matter. I don't think I'd at all feel guilty taking their money for something I've just scribbled up with my tablet, which is why I'd like some advice on what to charge. I'm seriously contemplating using my tablet as a way of earning some extra cash here and there. Nothing professional, but just a bit of dough on the side.
I'm aware there are other artists for hire out there who are infinitely better than I am, but I've been asked to do work for people, not them, so I figure if people like my work enough to pay for it, why not?

I've talked it over with some RL friends, who have told me that if someone was to pay for my work, they'd essentially be paying for my time and the right to do what they pleased with the finished product (Ie, use it anywhere). While I agree that it's my time someone would be paying for, I'm at a dilemma as to how much of a fee is appropriate.
What would you expect to earn at an average paying job per hour? $US20 minimum? So if we look at this like a paying hourly job at $20 an hour.... take my Dimitri piece http://lancerey.deviantart.com/art/Dimitri-Korsakov-139393088, that one took me around 8 hours, which makes the price $160, and that was ONLY a head shot.
That sounds pretty damn expensive to me, and I'm aware that not many buyers would be willing to spend that amount of money on an image.
I'd like to do paid commissions eventually, but working out how to make prices reasonable without ripping myself off is a problem.

I guess I'm really asking, what would you expect to pay for a custom character image done by me? Bear in mind that I'm always improving my skills, so my earlier works aren't an accurate representation of what I'm capable of now. (Hell, I used to paint with a MOUSE!)

I'm http://lancerey.deviantart.com if anyone reading this would be kind enough to take a look at my work and give me advice based on what you see.