Carrying an e-bike up the stairs will be a workout. Motors and batteries (at least the kind that can handle the range/hills you describe) are heavy. You're looking at about 50 - 60 lb assuming you start with a 25 - 30 lb bike. Price wise you're looking at $1300+ for a decent kit that can be installed with relative ease by a typical do-it-yourself-er. I have first-hand experience with the kits from ebikekit.com and found them to be good quality. Buying direct from China is cheaper, but quality (and even delivery) is a gamble.
Keep in mind that if theft is a concern, e-bike batteries are a nice juicy target. Look for a system where the battery can be easily removed and taken with you when you park the bike.