Many people have shared with me that there are free middle school and high school textbooks available through Amazon's Kindle. You can start your search here. Thank you to the people who shared it on Facebook and those who sent it to with me emails and text messages.
I like having many resources on hand to draw from because all of my children learn differently. While one explanation or set of diagrams for a concept might work for one child, I might need different graphics or find another way to explain it to their sibling.
Many Christians homeschooling parents are concerned about things their children can encounter in secular textbooks. I am too. I have an easy solution. You homeschool because you want to be active in your children's education. Pre-read the lessons and use what fits your convictions. You don't have to use all of it.
Free is free. Have a thankful heart, not a critical one.