but you have to be fast. I once saw a user selling it for just under retail because they were moving, and it was gone in like twenty minutes.
Other than that, set up price alerts on CamelCamelCamel for Amazon. The price for these box sets fluctuates wildly, sometimes dropping by almost forty percent during random sales, especially around non-major holidays. I got my 'Baroque Works' set that way last President's Day.
Don't ignore used book marketplaces like AbeBooks or even eBay, but scrutinize seller ratings and condition descriptions like a hawk. 'Like new' can mean anything. I always message for pictures of the actual corners and spines. It's a bit more legwork, but you can find sets from collectors upgrading to a special edition for a solid price.