You'll need a chunk of cash upfront for the insurance on your plane. An old 172, for instance, will cost over 4000/year if you want hull insurance. Plus, the airport you are at may require a general liability policy costing $1,000 or more. Ask the airport manager for details. Then, you may need a business license and many states require state licensing for commercially operated aircraft. Want to do sightseeing flights too? Then you need a random drug testing program, and make sure your mechanics are on it too. The costs can add up, but it may still be worth giving it a go on your own.