Well I know my friend Arrow started out with like 10$ conbadges and stuff like that though she was really underpricing the work she was doing. I'd look about and see what some of the other lesser known artists around here are charging to get a good figure though I can see the freebies you have been putting out to go for 5-10$ (10$ sketches seems to be a popular thing atm) depending on number of characters, colour etc. you might be able to get away with more though as I said check around and see what others are doing for similar work.

well id go small (price wise)
but i would like to see some of your colored work
your really good so you would sell

this is how i charge, since i'm still getting kinks worked out and stuff

first so that everyone can see, make a journal with all of your price info and stuff and then link it to your main page, like in the info section where your name and stuff like that and edit things if they change. ^__^

as for prices mine are as follows:

badges:
b/w = $1.00
color = $5.00

sketches:
pencil - $10.00
ink - $15.00
color - $20.00

full pieces (meaning pieces that are larger than 8x10 or have backgrounds and stuff, thus require alot of work. I charge by size of paper and effort put into it so cheaper tends to be smaller)
B/w - $20.00 - $30.00
color - $30.00 - $50.00

just for an example since i'm kinda in the same boat as you, so good luck sir! i hope this gives you some ideas.
Also look at other artists and see what they're charging, but try to start low since you are starting out. also dont forget to consiter shipping charges and what not if a piece is huge and you decide to like frame it and what not.

hope this helps~ ^__^

oh also, don't forget to put down what your perferred method of payment is like cash or paypal. ^__^v

I'd say give your work a reasonable price but still affordable, setup a payment method that works, and make sure to have examples of your work for others to see.

Also, you should think about setting a limit on the # of commissions you accept so you don't take on too many at once and keep people waiting for long periods of time.

When you figure it out please let is know I defiantly want a spot.