I've moved 55 gallon barrels of water all by myself. That's about 500 lbs.
The key is always leverage. In the case of the barrels, I tipped them on edge and rolled them. I even dropped one, and was able to get it upright by myself.
880 lbs sounds like a lot, but probably 2 of you can move it easily, if you work smart.
Get some round plastic rods to roll it on - tough ABS pipes would work.
Rent a good dolly, get some straps and you can easily lower it down the stairs too.
The trick is to not handle all the weight. Example - I assume they will take the safe out to your truck.
If the safe is sitting next to the tail gate, you tip it over and rest it on the edge. Now 2 of you can slide it up into the bed, since the truck is taking much of the weight.
Hell, I can move my 1300 lb safe around the basement a bit by myself if I need to. Tip a little, rotate, etc...