I always encourage hiring a music supervisor early on in the process, especially if you don't have a lot of money. When you bring someone in on post-production level and you got five weeks, it's really hard to organize lots of inexpensive music at a short period of time. It's possible, but it's really hard. The earlier you bring someone on before you start to shoot will make the life of the production, musically, so much easier. Fees are determined by the size of the project, the budget of the project, and what the music fees are.
Every director is different.
What I try to do first off is speak to them musically. From there, you establish what the pitfalls would be. For example, you have an independent film and it's a period piece. It's a really, really difficult thing to do with no money or a very limited budget. It's much harder than doing something contemporary, East Village, New York so to speak.