I would suggest that you simply take 50%, or some other large portion of the project, up front. Then, as you near a milestone, ask for another piece of it.
Billing at the end in one large chunk and then charging enormous rates just means you're not de-risking on the on set, and you're screwing a customer relationship.
Also, industry norms are NET 30, and some customers may even operate, and push, on NET 90 terms.