well i honestly have no idea about pricing, but 50$ seems sooo cheap really.
i like this girl's art, and stumbled on her deviantart from a gaga forum... look at her prices http://thegirlinthebigbox.deviantart.com/journal/23405780/
oh wow, she's good. thanks for posting that, it gives me a rough idea of what to charge.
Keep in mind that she's also extremely famous (as much as a dA artist can be, I suppose), and she can afford to have very high prices, so it might not necessarily reflect the time and effort that she's putting into commissions/art.
My suggestion is to find out about how long it takes for you to draw a detailed bust, and charge hourly. (http://setsuna22.deviantart.com/journal/34173464/#comments
sorry, couldn't get a workable link without redirecting to the comments... I haven't had my coffee yet)
If I were to open commissions for my digital paintings, let's say... it takes me about 6 hours to paint a shoulders-up bust. Being a relatively new artist and not as good as you or as famous as Marley(girlinthebigbox), I wouldn't get business if I charged $10/hr. Reflecting my newbieness, my price for a painting of a bust should be about $5-7/hr, plus the cost of materials (negligible, since it's just electricity and the G5 doesn't use that much power).
So I'd say for you, start out on the high side. More than $10/hr, probably, because of the amount of detail you have in your drawings. Find out about how long it'd take, and figure out a materials charge, then even it out to a nice sounding price ($48 change to $50, so on and so forth), and be prepared to explain to potential commissioners why you charge the prices you do.
But that's just for commission. If you're selling a work of art, you should charge a considerable amount more. Again, find a price per hour (one of my friends charges $200/hr, she never sells anything), find your materials charge, and then tack on a nice honkin' charge for good measure. For original works of art, the sky is really the limit. I'd say $500 for you (depending on size) is definitely decent, but if it makes you feel more comfortable, check out Etsy and see what they're selling original drawings for.
And definitely copy the drawing and make high quality prints. DeviantArt has a decent printing section, so you can sell prints through there as well (the bonus is that you can choose different sizes with different price points). Also, you can sell prints with less overhead by printing them yourself and mailing them yourself.
What you should definitely consider is collecting copies of your work (that isn't available to view online) and having art books printed. Comixpress.com has really good prices for printing books, and they are really good quality... and if you don't want to buy 50 books and try to sell them yourself, you can just have one printed and then set up an online store through them.
I also highly suggest finding a gallery that will show your work before selling them. Get your name out.
Uh, long post is long.