I don't know if this will help you, but I charge $3 per card, no matter how much or how little work goes into them. That doesn't begin to cover time and materials (probably because I can't stop buying beautiful dies, etc) but it seems to be the amount that people don't mind paying for a card that is so different from the "Hallmark" style. The people who buy and appreciate my cards usually buy 5- 15 at a time and a few have almost made me cry when telling me who they will be sent to.
Most people have no idea how much work goes into making a card and treat them very casually, but those who do appreciate them really love them.
The crazy thing is that I have a hard time convincing myself to offer them for sale to people I don't know. I put so much of myself into them that I don't like "strangers" touching them. I do put them in clear card covers so they don't get messed up , but if I really like a card I want to keep it or have to make copies so I have one. So........... I have dozens of cards sitting around here and always new ideas floating around in my head. I feel fortunate to be so obsessed by something that always feels new & interesting ! Now, if I could just let more of them go !