That's a great price for any 450lb. safe do you have to be a member of Cosco to get it?
Yes, COSTCO is a membership type store, but it's not expensive IIRC. Certainly less than the $200 savings on this safe.
BTW, they deliver to your curb. That means they will drop it off at the end of your driveway. After that it's up to you. When they delivered mine I asked the driver if he would mind rolling it into my garage. I have a short, flat driveway, so he put it in the garage.
It's not hard to move with a good hand truck. If you need to move it up/down stairs, the door is easily lifted off, which will reduce the weight by about 100#. Have a young, strong friend available to assist. (watch for the ball bearing that will fall out when you lift the door off