Make sure that your contractor is including a cost to service all types of circumstances. These are situations like low and high accumulation, potential for snow storage removal, an option for salting, or even any irregular services such as there is a special event going on that your property needs special attention for.
The worst situation to be in is when the words “I don't do that” or “that wasn't in the contract” come up. These things should be sorted out in the bidding process.
The right contractor may not always be the cheapest. Ask yourself, is this cost going to give me the value I want? Or is this not enough to do the right job.