Thrift stores and yard sales are my best friend. You can find all kinds of textbooks and tools for using in homeschooling.
Most of my worksheets I get free off of the internet. There are a ton of websites online where you can get free homschooling worksheets to print off and there are free online cirriculum to use, The one that we use a lot of is the Easy Peasy All-in-One Homeschool. It is easy to use and has everything. You have to check out Pinterest also. It can take days to go thru all of the free homeschool items on there!
We also use the library a lot and find out what is going on each month in and around our town. Last month was busy with Halloween stuff to do around our town and it did not cost a dime. It is also easy to turn anything that you do into a learning experience. Like going to the grocery store teaches reading, math, budgeting, health, and more. Go to the park and learn about nature, science, weather, and more.
You just have to keep an open mind about how much it should really cost to homeschool. I know some people who go all out and spend thousands a year, but you don't need to do that. Just hunt around and search online and you can find tons of free homescooling stuff. Fun stuff also.