You're going to get a lot of people saying "$0" when you ask a question generally like this because most people (especially among artists who can do the work themselves) are just not interested in commissioning artists to begin with.
What you should be thinking of when you price your work is what is a fair price for what you put into it. So ignore insulting advice like charging $0-$5 for stuff that undoubtedly required an investment of your time and resources.
Make sure you're covering time spent, and you have a right to pay yourself minimum wage in your jurisdiction. Now yes, in evironments like DA there is little opportunity for much except quick cheap sketches because it's full of kids who don't have much money and don't know the value of it. So to avoid selling yourself short, come up with a type of work that you can knock out relatively quickly to keep your price down. Example; charging $10 an hour but your watchers think $20 is a fortune? (bless their socks) Don't spend any longer than two hours on the type of work you sell to that audience.
It's tempting to join the downward price spiral and think you have to beg for pennies, but ultimately this is bad for everyone concerned. There's no magic price at which a work will become saleable, yet decreasing the price increases audience perception that art is wortless. If you genuinley can't sell your work at a fair price, then instead of devoting your time to people who don't appreciate it, devote your time to working on your skills (both art techniques and marketing skills) untill you get to a place where you CAN sell your work fairly.
I can't see many helpful answers here, unfortunately ._. I like your art, although I think you may want to upload some more, so that the comissioner knows better what to expect. I like your gallery, but if you're just starting out with comissions I'd suggest price range between 0,5-6$, and then gradually rise them. It's better to get some more people interested for cheaper at first and then, eventually, gradually add to it. Hope I helped
You might be able to charge around $20-30 for a full-color drawing. I'd say work on your lighting and anatomy for a bit, read lots of tutorials (the ones in ImagineFX are great) and then you'll be looking at more.
I agree with raiyneofgailin, and would also add that you need to submit more drawings with varied lighting, poses and expressions, the ones you've submited so far look very similar. People will be more interested in your art if you show them that you can draw "anything".
You should practice gesture drawing, there are some useful sites for that, like this [link] and this [link] (but beware, the second on contains A LOT of nudity). As for the rest (lighting, body proportion, anatomy, etc), there are lots of tutorials over the internet. I also like to practice by "copying" photographies, like my avatar, which is based on this photo [link].