Anonymous wrote:you need to dig down the floor rather than raise the ceiling.
6'6" is very low. And PP is right about digging down the floor. That said, doing so will be very expensive as well. If you are not planning to stay for many years, you will likely not recoup the money when selling. If you can't afford the digging and just want to do some basic finishing for your own enjoyment, go ahead, but don't spend too much -- finishing it with such low ceiling will not make the house more attractive; just do it so that you enjoy the area a bit more, not because it's a good investment (it's not)