Well, If it were me then first I would check out other people with similar art styles to mine and their prices, see what they offer, compare quality, making notes regarding offers and prices. Keeping in mind that, I think about the time that it takes me to make a specific work, about my needs, if I have to pay my roof, food, etc.
Some charge differently depending if they are doing only a face-to-bust, or face-to-the-waist or a fullbody. As well some other people charge depending on extra characters, type of background, if it's simple or detailed. Some may charge extra depending if it's for personal/non-profitable use or if it's for commercial use.
In my case I don't charge for the type of use the clients gives to the drawing, nor if it's a fullbody or a bust.
I recently changed my prices, but cel shaded work was $40 USD a character, $25 extra character and $25 background. So $90 USD. Here are some samples
In my case I work with images around the 4500 x 6750n at 200dpi which I give to the client once the work is both paid and finished. Then I use a smaller version like these ones to show the work online, with a watermark. The client however can do whatever they want with the picture, even sell prints or whatever, I don't mind.
As I previously mentioned, those were the old prices, now a work like this is $50 main character, $30 extra character and $30 background. $110 USD. I have to increase the prices due to my country devaluating the currency, again. personally speaking I fidget a lot when it comes to increase the prices but that's why is important to keep in mind your needs, your overall situation, the time it takes you, and so on.