I know that Waverly Hills Sanitorium allows overnight investigations, and multi-night investigations. I think the cost is $100 per person, 20 person minimum. So I think the cost would be roughly $2000 per night for a team.
You can get details here:
www.therealwaverlyhills.com/Tours/
If you're an established team, you can get into quite a few locations. Most of the "Popular" ones will be at a higher fee though. I would tend to look for the unknown ones. Why be a tourist when you can be an explorer.