UPS DC-8-71/73's were excellent airplanes. They were all converted to glass cockpits. Any of those resurrected from the desert would be a reasonable choice. The -73, with it's long wing, extra fuel and higher GW made the best freighter. The -72 has the same wing and fuel, but it is 30 feet shorter, and there aren't many around.
As far as operating costs, they burn 12K/hour. With experienced maintenance they can be a very reliable airplane. UPS went with 767-300ER's as replacements and the operating costs were less.
Simulators in the U.S are becoming a difficult proposition. No Level C's left. Pan Am's in Miami is not operational, and may not be again. There's one in Cincinnati and one in Wilmington. I don't know what happened to the UPS -71 sim (with matching glass cockpit). It was a good Level C.
I'm just a pilot, and not a bean counter, but the DC-8 has soul and character compared to what can replace it today. Too bad they're a dying breed along with the folks who flew them worldwide.
Good luck with your endeavor.