How much does it cost to launch a satellite into space?

How much does altitude affect cost? (e.g. low-earth orbit or geosynchronous orbit)

I realize a lot of the number are going to vary on payload but I’m looking for as many different examples (especially on the low-end of the cost spectrum). If I could get an empty payload cost that would be ideal.

Also, how has price changed over time? Is it dropping rapidly or more or less staying the same?

Bonus points:
1. What kind of time frame is involved for launching a satellite?
2. How many locations can used for launching satellites? Is it only a handful of sites or is it just about anywhere?