Invoicing is part of my monthly ritual as a freelance writer. Typically, I do my billing on the last day of the month. Seeing as the 31st is Halloween, this month should be extra scary. Scary may be a little strong, but, truth be told, I still am not comfortable putting a price tag on my services.
That's why I found this month's Writer Magazine so helpful. Lola Augustine Brown's article "Show me the money" highlighted common arguments for for writing for free and debunked them.
In a nutshell: "Professionals do not work for free. Period."
I like that.