The reason that he might have saved more than you is the region that he live in as opposed to your region. Different areas of the country charge different rates. I live in Alaska so getting some materials will cost more. Dumpster fees sound about right. 500 to 600 to drop, fill, and dump. I work at a large roofing company so we add to the invoice accordingly to cover labor, material, and any overhead(vehicles,office,yard).
Again, different areas = different pricing.