Alice, on the engine portion of yer dilemma. The "older" units will have an nhc250, inline 6, non-turbo, engine that is 855 cubic inches ( 14 liters ). Next step, same engine, with a turbo. Next step is the 6ct series. Only 8.3 liters but same or better power due to electronics and modern design. All are rock solid. ( Commercial Cummins diesels are world renowned for their durability, sorry, I am not a salesman, and no Holiday Inn Express, but they are nearly bulletproof if cared for properly). Watch miles and hours on the clocks. These were low frequency, hard use machines. Maintained, but used for some very tough work. Whatever ya choose I hope ya love it and it gives ya love in return. I truly believe that. They know, deep down in their chassis, they know.
That auction stuff sounds fishy to me too. I am super lucky. Found my dream girl only 60 miles away from a "dealer" kinda place. Prolly nothing like that "up there". What part of the Great White North are ya in ? Be specific, in your location on your profile too. "They" are watching. Hehehehehe