Wasn't responding to your post in particular but I was prompted to respond after a shoot yesterday for a client. She actually told me that, in her opinion, I had completely under-charged her (doh!) and thus the difficulty of charging and the concept of self-worth is very much on my brain.
My client was an artist so we got into a discussion about how she prices her paintings and does she find it difficult to do that. We both agreed that it an extremely tough part of being a creative person, trying to place a value on what is essentially time and basic materials. She now lets an agent handle all that but she admits she baulks at some of prices he sets. Made me think about how little I charge sometimes and yes, a print does only cost $0.50 but in reality, there is so much more to it than a piece of paper and inks.
Anyway, the good thing was she gave me an additional $100 on top of what I asked. So I figure my work is worth a bit more than I think and just maybe everybody else's is too.