The base Ring Protect bundle starts at $199 and includes a base station, keypad, a contact sensor (for a window or a door), a motion detector and a range extender. Presumably, you will be able to buy more sensors and keypads to add onto your system, but Ring doesn't have them available for preorder on an individual basis yet.
The Ring Protect is designed to work with existing Ring video doorbells and security cameras for a seamless home security experience. It's $10 per month (or $100 per year) for cloud video storage for an unlimited number of Ring devices plus 24/7 professional monitoring and cellular backup (if you have the Protect base station). That's not a bad deal at all, especially if you already own Ring devices.
The Ring Protect bundle is available for preorder today at Ring.com, BestBuy.com and HomeDepot.com. It will be available for purchase in Home Depot and Best Buy physical locations later in October.