There are different delivery fees and services offered from store to store. You may save some money in one store just to find out they charge twice that amount for delivery. There are plenty of stores nowadays that offer free local delivery, and if they don’t you can always negotiate for it. You should expect on average 4 hour delivery window, where you are required to be available within that timeframe.
There are also different types of services associated with delivery. Some stores offer full delivery and set up in your bedroom, while others will drop the product off on a sidewalk by your house. Often there could be a surcharge for a delivery upstairs.
Unless you have a new home for your old mattress, double-check if removal of your old set is part of the delivery service. Some retailers charge a fee for pick up and disposal of your old mattress set.