Music is one of the last things, so it often gets what is left, both little money, and of course what little time is left - "We can give you 3 days to do the score."

There are so many options, though. I belong to Production Crate, for $5 a month. You can download visual effects and as many music tracks as you like. Though I compose, I grabbed some tracks for a project that I was editing, just to get it finished quick. It was for somebody else, and they were asking for a ton of re-edits, so I gave them the free (er, $5) fast score.
Ideally, you want a dedicated composer. Some people do it for cheap or free, but you should really pay them something. What is paid usually depends on the project - no budget indie, some budget, medium, pro, etc.
My question for you is, what is your budget? Did an investor give you a blank check?
Someone is giving me 10K to make a bigfoot movie in August, so I took that budget and applied to what was absolutely needed, such as 3K for the bigfoot makeup. I already have equipment, so aside from 3 hard drives, I figured what gas, food, and permits cost. Are you paying an editor, or DP (I'm doing those)? How many crew do you need? I have that down to 4 people. How many actors. I've got 12. Uniforms? (4 rangers, 2 sheriffs, 1 deputy).
Again, I have equipment and am covering post, so I can divide what's left to give the actors and crew a small amount per day. I have 7 days budgeted. I figured approximately 9 (crew/actors) per day X 7 days = 63 wages. If you can, budget a certain amount for contingency. Something unexpected, always pops up. 10 to 15% of the budget would be wise.
Are you making a feature? You'll probably need to add E&O insurance, and Title search costs. Many people budget in promotion costs, such as artwork, film festival fees, advertising, etc..