The chalk paint wax is super expensive, what else could I use?

You can put a clear sealer or poly over chalk paint. However--if you have waxed a piece you cannot poly/seal over wax. However--you can wax over a clear sealer or poly.

https://www.diybeautify.com/2017/01/top-coat-protection-options-for-chalky-painted-furniture.html

Hello Char! You will be glad to know that you can make your own inexpensive chalk paint. Click on the link below, which will give you access to the recipe. Good luck and enjoy!

https://www.lowes.com/creative-ideas/paint-stain-and-wallpaper/diy-chalk-paint/article

I have made chalk paint for several projects, wood and metal. I sealed them with an old can of paste wax I had. I think it's meant to be a furniture polish. I put it on with a rag. It takes chalk ok and cleans very well. Hope it helps. Good luck.