- (free) set up google sheets (not sure if this is required but that's what I do)
- (free) run an scheduled appscript bound to that sheet with regular intervals
- make it scrape the page (it's just javascript, you can do get requests, etc)
- Have it scrape a webarchive of the page you want to compare (not need to persist state or run a database, etc) and have it check the differences with the current page
- Have it send you an email if there's changes
It's totally free, takes no time to set up, and is relatively effortless. It can even send you alert on failures etc. I do something like this for my reading tracker where I crawl various sites (like amazon, etc) and RSS feeds for new releases of books/series I read and collect them in a dynamic spreadsheet.