Yes, I do require you to pay up front.
The reason for this is that I'm in high demand and want to make sure I reserve time in my schedule for the writers who truly want to work with me. By paying in advance, you're making a commitment to both me and yourself that we will work together. That way I don't find myself with gaps in my schedule that could have gone to another writer.
The cost is $4.50 per page (8.5" x 11" or A4 page, double-spaced, 1-inch margins, 12-point Times New Roman Font).
If you don't know exactly how many pages you have, that's okay. Estimate as best you can—if you end up sending fewer pages, I'll either reimburse you or give you credit for future pages (your choice), and if you end up sending more pages, you can simply pay the difference when you send your work.
The sign up form allows you to choose the number of pages.