Marina from Fancilful Devices recommended a post from Penny at Sparrow Salvage about pricing your work. Actually...it has a lot to do with valuing yourself and your work. It's an interesting and timely article. I've quick linked Penny's blog so you can check it out for yourself....it makes sense.
I also found this on Etsy about Pricing Your Work. It's a whole lot duller than Penny's post but also pertinent to the process.
It's just an issue that is never going to go away but it can be looked at and worked on from many different angles.