Be very, very careful on this. I have been doing overnights for nearly 15 years. I was naive at first, as I had several nice overnights for 12-15 hours as Benjamin Nicholas stated for anywhere between $500 and $1,500. The cheaper were off Craiglist, but were just as good as the $1,500 ones. Most of mine were around $1,000.
Fast forward to today. I've had several escorts from south of the equator want between $1,100 and $2,000 for an overnight. However, when you finally start asking start and stop times, these South American escorts seem to think that an overnight is only 5-6 hours. To me, that is an extended session, and not an overnight. More that one even had the audacity to ask that I buy them a hotel room for after the overnight. "After the overnight?" I thought the overnight was "over the night". To each his own though.
Always ask what constitutes his overnight, and what his limits are, and what your expectations are.