PAY WHAT YOU FEEL
I never want my clients to feel stressed about the "cost" of my work. The truth is that I honestly don't know the value of my work as it applies specifically to you, so I just stopped trying to guess. I think that paying what you feel (and WHEN you feel) frees your mind of anxiety and expectations while I'm actively photographing, and increases your joy when you have the finished photos!
ONE SMALL CAVEAT
For photography services that require a contract, I need to be paid for said contract to be valid. I generally set that amount at $100. It is refundable and negotiable. This way we both have some skin in the game.