I had ducts cleaned last year. It was a truck with inflatable bladder type things in the truck bed. Noisy. I thought it would be done from each vent but it was actually done from the heater (furnace).
There are different thoroughness though, one they go in from the vents, and brush out the ducts of debris (particularly from new construction).
Though new construction, the price dictated I do the super duper vacuum job. It seemed like a good idea and I am glad I did it.
Prices varied but it seemed the process was similar, and a competitive field. Try Angies List or Yelp too.