I price mine around the amount of time i take to the artwork. Something around $15 an hour. If business is slow ill make a sale so a little cheaper. sometime have to fluctuate with the market. Id say your colored piece looks between 40-60 range
Since you're doing digital, it definitely depends on the time spent doing it. Since I've been doing art for 10+ years and I have a degree, I tend to try and charge anywhere in the dollar-a-minute range (usually less), but I tend to work quickly. It also depends on what others are choosing to charge as well, and unfortunately in the furry fandom I see a lot of under-charging. Remember, a low price is not necessarily good-- it tends to communicate either desperation, naivete, or a lack of self-worth or quality of work, which aren't things commissioners/customers feel good about. "Well... why is this so cheap...?" It can work against you. It may take some trial and error to see what people respond to. Best of luck!