Might buy low mileage 6.9 idi

I've wanted a diesel truck since middle school. I found an 80's Ford 350 van 6.9 idi low mileage, supposedly only rolled over once and currently at 110k miles. He maintained it well, it's a 3 owner vehicle. He's okay with me taking it to the mechanic to have it looked over and all that. He only wants $3,000 for it, but I'm sure he'll take less. Says it cranks right up and shifts smooth. I understand that diesel engines are more expensive to work on, but by how much when compared to gas engines? I understand that the better milage of the diesel engines isn't much of an advantage because the diesel costs more. Does the engine going around 500k miles offset the price of repairs when compared to a gas engine that lasts till around 250k miles? I'd leave it stock, other than the exhaust, a better air filter and a couple other upgrades to bullet proof the 6.9 idi and reduce the potential for engine failures. Any advice would be GREATLY appreciated. Thanks