https://www.cnet.com/news/free-camera-and-save-15-on-a-simplisafe-security-system/

At a bare minimum, you'll need the SimpliSafe Base Station and Wireless Keypad, which together cost $185. Alternately, you can start with the Foundation Package ($195.47 after discount), which includes those two items, an entry sensor and a motion sensor.

Next, choose a monitoring package, which is based on a cellular connection -- meaning no landline or Wi-Fi required. These run 50 cents per day for Standard monitoring or 83 cents for the much more robust Interactive option.