What drives the price
Stories and access (ladders vs lifts), siding material, how much scraping, caulking, and priming is required, and the number of colors and trim details.
Paint itself is typically 15–20% of the bill. A quote that's cheap because of cheap paint is saving you very little.
Prep is the job
Wash, scrape loose paint, sand edges, replace failed caulk, spot-prime bare wood, repair rot. A quote that doesn't list these steps is quoting a shorter-lived job.
Before you sign
Get the number of coats, the paint product line by name, surfaces included and excluded, and the workmanship warranty in writing.