Let's say there's a $20k difference between a 150k mile rig and a 50k mile rig.
Chance of major, engine or trans, failure. $5-10k per component.
Brakes, axle seals, front end, engine components like AC or radiator, if you don't know how to wrench on stuff, all those things are basically $1000 bills each time at a repair shop.
Heck, I've got my 1/2 ton work truck in the dealer for some warranty work and asked for a price for new shocks. The shocks I requested are under $400 shipped to your door and it's a 2 hour job, especially at a shop on a lift. Quote was $1200 !
I just laughed and told the guy I wasn't planning on paying rent on the loaner truck and part of the warranty repair to get new shocks.
Point is, if you have to ask the question, you don't understand vehicles and you'll spend the extra money either way, likely.