You can try calculating by dividing the number of pages with man hours
I charge between $10 - $12 / pg for freelance clients, and get about the same with companies (between $8 - $ 25 / pg, depending on company and time of year). Overall, I am not complaining but I find I began to weed out some of the private clients in favor of companies... sometimes it was better pay, and other times it was easier to get the money. I didn't know people charge up to $35/pg! If a page takes me 15 minutes to write, I feel like that's a bit much...
Maybe I am selling myself short... I have a M.A and a bachelor of Education. However, I just started doing essays about a year ago (started with private clients.. then worked my way to companies). I work for 2 low - medium paying companies and one high-oaying ($16 - 25 or even $33 / pg, depending on reason).. as I've mentioned. I'm a good writer and consider myself as such (perhaps not as experienced as some of those here.. won't lie about that). I'm thinking for the coming year I remain with companies, and begin charging private clients a solid $15 / pg or the workload will become too high again - like it was in Feb, March and Apr of this year.