Use coupon code BEGINNINGS for $10 off anything in the Dungeons & Dragons Beyond marketplace. Limit one use per account.
This is the cheapest price yet for the campaign adventures. The previous sale D&D Beyond ran was $20 for any book, so the $30 sourcebooks are the same sale price with this coupon, but the $20-25 campaign books are cheaper with this coupon.
I personally prefer buying the campaign books on Roll20 because they're loaded into Roll20, but the cost difference is significant. Roll20 never has sales and charges $50 for them, while you can buy Tomb of Annihilation on D&D Beyond with the coupon for $15!
The Tortle Package is $1.99, which is a digital only offering. That's probably going to be the lowest price ever on that.