When you charter a private jet, you are billed an hourly rate multiplied by your total flight time and some incidentals if there would be any.
For private jets, hourly rates may vary by size, class, and type. There are softwares available as part of the plane which calculates your total flight time and considers typical air traffic control routing, seasonally adjusted wind patterns and aircraft performance criteria.

Depending on your trip, additional costs or incidentals might include landing fees and airport usage fees, overnight fees to cover the cost of housing the plane and crew if your trip is longer than one day, and International fees if your trip leaves the country. These costs are added to your total bill.
private jet charter prices may vary by date for the same trip because availability varies by date. Included in the cost of your charter are ferry charges, which are incurred when an aircraft is based at an airport different from your departure or arrival point. If a plane has to travel to cover your charter, it will alter your charter cost. That said, there are many ways how you can do budgeting for your travel and you want to fly via jet charter.