Mileage is one thing but how well was the engine cared for is a bigger factor. You can have an engine that has a zillion miles on it and not use a drop of oil between changes or you can have an engine with 50,000 miles on it use 2 quarts between oil changes. It really boils down to how well the vehicle was maintaned. Also what was the truck used for that may have a big factor in it as well. Was it worked hard for those 246,000 or was it driven unloaded, no pulling for 246,000 miles down the highway. The 7.3L is a durable engine. I say if it runs good and drives good have it checked out by a mech. If your a premium member get an oasis report on the truck. Make the decission for yourself. If you race cars I am sure you can tell if the truck is worth the price and if the truck will last you for the amount of time you plan on owning it.
By the way welcome to the site.