Every business will vary by contract.
If you'd like a high level overview on how business is handled in the consulting world, I can chime in a little there... At least in the field I'm involved in:
Whenever we contract out to a 3rd party for our clients, we typically factor in a 15% cut right off the bat (e.g. My contractor will charge me $1, so I'll pass over this charge to my client at $1.15). We also pass over all expenses, per diem, etc. to the client as well, as part of the required expenses for the project. Then for the consultants (me and my team), we'd charge them our standard billing rates, along with a budget hours 'not to exceed' for everyone involved in the project.
If ever we go over budget, that's when the change orders come in (as long as it's justified, of course! Like client-driven scope changes, unexpected circumstances, etc.). So this is where the company makes their money from the project.... Within us consultant's billing rates, my salary is literally fraction of that. So the remainder of our billing rates is overhead, profit, consumables (office, materials, etc.), etc.
Shopping the Greater Denver Area, Colorado Springs and in-between in Colorado. 33 year old male and willing to travel!