Big outfits usually have a set price contracted throughout either the calendar year or fiscal year. It's sort of like Southwest Airlines fuel hedging: you commit to buying X tons of material at $X price in throughout the year in exchange you have a fixed price for the material.
Now, I don't know of any companies who have extra material from the job 'left over' because if I were estimating the job, that would be accounted down to the truck. You have the cost of getting the spreader to the driveway, the cost of trucking at least one roller, plus the support truck with the plate compactor, hand tools and emulsion buckets.
You're not just pulling a highway spreader, which is at least 10 feet wide, off a highway job and running it down to someones house to do a driveway with an extra truck. Frankly even with a heated dump body, you wouldn't want the old asphalt that was hardening in the truck for two hours reheated in the spreader. The size of equipment for highway work dwarfs the size of the equipment required to do most residential driveways. Of course, I'm from an area where a 10x600 foot driveway would be really long, not unheard of, just really long.
Hire someone local who is in the business and does driveways for a living with a local phone number and address.