Simple tool for tracking ASIN search term performance?

Can anyone suggest some good tools to do this? I just want to see how my ASINs rank over a given set of search terms, over time. Ideally displayed on a simple graph.

E.g Imagine i sell an alarm clock product, I’d like to see in what position it shows up when a user searches “best wifi alarm clock” on Amazon.com. And I’d like to see both “live” position and historical positions.

The goal of course is to have visibility/tracking on this data so I can work to improve my ranking over time.

This is a feature of a lot of larger products (e.g SellerApp) but outside of the free trial I’d have to pay 99 USD / month ! Seems excessive. I just want simple and affordable.