Blu-ray.com always lists the lowest prices on discs too. So thats a good place to check for best prices. If the Amazon tracker doesn’t always work
I always start there, to check specs, quality, reviews, etc. I have also been using 'CamelCamelCamel' for several years, which I imagine works like Amazon tracker - I put in a desired price point for each disc I'm interested in, and it emails me when it drops below that level. Seems to work well, with no spam or other problems with it.