Probably $20,000-$80,000 depending on condition and how complete the project is. Engine core is $10,000-$15,000, overhaul about $30,000, prop is $8,000-$13,000 in overhauled condition.
If it takes 5 years to restore and you are paying $500 a month in hangar rent, that's $30,000 just in storage space.
Keep in mind that a T-6 has two of everything, so there is more to restore than in a P-51. T-6 parts are only available from a few sources in new old stock condition, and used parts may be worse than what you already have. New rubber seals are available for most everything from hydraulics to canopy seals. Start with the best project you can find if you really want to do this.
T-6 is easy as far as sheet metal work goes, but the skins are thin so you'll neet to develop a good technique to keep from deforming the structure when you shoot rivets.
Here are some photos of my project and the restoration I've been doing:
http://community.webshots.com/user/c322348
I started out with a relatively complete airplane with no corrosion. There have been a few surprises, but nothing major. My time is limited, so it has taken a long time. I probably have another couple of years to go yet.
My advice: If you want a flyable airplane, save your money and buy one. It will be in your hangar sooner and will be cheaper. If you are truly looking for something to work on, you will get your wish. it will be a lot of work!
