I understand these are expensive to buy. Here are a few options for you rather than buying them new
The Big Ideas website allows you to access the book, take practice tests, and play games to practice your skills. In order to login you need your school username and password. Use the link that says "Login with Clever".
Big Ideas Math Videos
This app has videos explaining the different concepts in every lesson of the book
It is free and you don't need a login to use it
This website allows you to pick your subject area and topic you want to learn about. Once you have decided what concept you want to look at you can watch videos and then practice that concept. It will even tell you your skill summary after you so some practice.
This is a free app and is extremely easy to access practice problems and videos!
Ch. 7 Extra Practice