Commissions for a new cage

[BirdSquawk]

So I feel pretty confidant in my bird related art skills and was thinking of opening commissions so I could buy Jack a bigger cage. Is anyone interested? One example of my portrait/avatar style is my current avatar, I'm working at developing a few options for people. Payment would be through paypal.
One question I have for people who have done digital art commissions: are there any resources for how to accurately calculate prices? I want to be fair to myself but also competitive with current trends.
Thanks for looking, and hopefully I'll be able to draw your beautiful birds!