Keeping your humble abode secure has never been a particularly cheap proposition, but it's becoming less spendy with this new wave of internet-connected cameras and sensors. The Ring Alarm security kit is already priced competitively at $200 on a normal day, and it's even cheaper now. B&H will sell you the starter kit for just $149.
This deal is for the smallest 5-item Ring Alarm kit. It's $199.99 everywhere else, but B&H has it for $149 ($50.99 off). The system comes with a motion sensor, a door sensor, a keypad control unit, a wireless hub, and a wireless range extender. If you want more sensors (and you probably do) or keypads, you can get them on the Ring site.
Keep in mind, Ring had a security snafu just recently, but the company has reportedly shorn up its policies following the Amazon acquisition. It's your call if you believe that, but the basic security system doesn't include any cameras. If you do still want to use Ring's cameras, they'll integrate with the same app.