5-Year-Old Class 8 Tractor - for $25,000

Having a Class A Commercial Drivers License in hand - I want to get behind the wheel of a 18-wheelers (tractor only) without taking a job.

Shocker #1 - a new truck runs $150,000 - That's a lot of money - It's like paying off a single family - starter home in 5 years.

Shocker #2 - a used trucks runs at fraction of new one - considering the expected longevity of a million-miles truck.

 Many of the 5-6 year old used tractors (with 400,000 to 600,000) runs between $22,000 to $28,000.  I wonder why these vehicles depreciate so quickly.  Will I be better off with an older trucks?

from  $25,000 - base truck
  add  $ 8,000 - transmission overhaul
  add  $10,000 - engine overhaul
  add  $ 4,000  - replacement tires
  add  $ 5,000  - other systems
===================
   Est $53,000  - as if new truck

There are many "integrators" - tractors manufactures, but the engine/transmission combination is total out of this world.  I don't know how can a brand of truck can be price cheaper than the others with the same guts.