Charter jet cost can vary depending on the size and type of jet, and where you want to go. For example, if you were to take a light jet - say, a Learjet, which seats about 5-8 passengers, from Boston to Seattle one way, it could cost around 20 grand, more or less, depending on the time of year and booking times. A medium jet - say, a Hawker for example, which seats 7-9 passengers, might cost about 30 grand in this example. A heavy jet such as is used for corporate flight trips - say, a Falcon, which can seat up to 15 passengers, might run in the neighborhood of 40 grand, more or less, and a turbo prop such as a Cessna which can seat up to 12, may be about 20 grand in this example as well. This would generally be the ballpark charter jet cost whether one passenger is going on the trip, or a full plane.
Obviously, the benefits of traveling by private jet outweigh the whole charter jet cost... for example catering and in-flight spa (in many cases included for free), pets riding in your lap or in the seat right next to you - which is truly wonderful considering that the United States Humane Society has recommended we never take pets on commercial flights due to harsh conditions in the cargo hold which lead to many traumatic deaths, security checks being much simpler and much less time consuming, and the total and complete lack of lines (you drive right up to the jet and go straight from car to plane), just to name but a small few.
Some may consider private ownership or fractional ownership of a private jet, thinking the cost would be more economical. This may seem so on paper, but in reality the upkeep costs, regular registrations and other hassles can be a continuing cost, both monetarily and time-wise. Further, even if you own or partially own a private jet, you will invariably end up chartering as well anyway. There are times when your jet may be down for maintenance, or otherwise unavailable, or it may not be the right jet which could serve your present needs. If you have a small private jet but need to take more passengers than it can carry, will you make two or three trips? Charter jet cost in this regard in comparatively much smaller, and instead of just one jet, you have 24 hour access to a fleet of many kinds 7 days a week, 365 days a year.