camelcamelcamel.com is a useful website for tracking amazon's prices. There are a few other useful tools like this.
Here's the record for the roomba:
https://camelcamelcamel.com/iRobot-Roomba-7150-Wi-Fi-Connected/product/B07GNRGDKP
There a few browser extensions that can also help you get the best price... wikibuy for instance. It will check the price of items in your cart and let you know if it is found cheaper elsewhere.