What changes the price
Paint condition
Heavy swirls need multi-step correction; new paint needs little.
Vehicle size
More surface means more time and product.
Coating level
Entry, mid and long-life coatings differ in cost and lifespan.
Extras
Wheels, calipers, glass, trim and interior surfaces.
Why cheap coatings disappoint
A coating applied without proper decontamination and correction locks swirls in and may not bond well. It looks fine for a few weeks, then water stops beading. The difference between quotes is usually the prep.