Here's an incomplete list of titles to which the 20% Funimation discount applies. I know for sure some of these are nowhere near historic lows. I'm not going to check each one to put it in here, but if you have any questions about a specific one, ask and I'll try to get back to you.
18 pages of listings. My eyes hurt.
A Certain Scientific Railgun S Season 2 Blu-ray/DVD(42.99 pre-discount)
Afro Samurai: Resurrection Director's Cut
Attack on Titan Season 1 Parts 1, 2
Attack on Titan Complete Season 1 Blu-ray/DVD($36.96 pre-discount)
Attack on Titan Season 2 Blu-ray/DVD($26.79 pre-discount)
Basilisk Complete Series Blu-ray/DVD
Black Butler Season 2 Blu-ray/DVD($32.46 pre-discount)
Black Butler: Book of Murder OVAs Blu-ray/DVD($24.79 pre-discount)
Cat Planet Cuties Blu-ray/DVD S.A.V.E Edition(14.99 pre-discount)
Code Geass: Lelouch of Rebellion Season One
Cowboy Bebop Complete Series Blu-ray/DVD($28.49 pre-discount)
Deadman Wonderland Blu-ray/DVD($19.96 pre-discount)
Death Note Complete Series Blu-ray($27.56 pre-discount)
Eureka Seven Complete Series Blu-ray($45.79 pre-discount)
FLCL Complete Series Blu-ray($24.44 pre-discount)
Fairy Tail Collections 1, 3, 4, 9, 11, and Zero. The collections between 1 and 9 might be on sale. Didn't check individually.
Freezing Season 1 Blu-ray/DVD($22.13 pre-discount)
Fruits Basket Complete Series Blu-ray($43.42 pre-discount)
Full Metal Panic: Fumoffu Blu-ray/DVD($17.99 pre-discount)
Ghost in the Shell Arise: Borders 1 & 2
Hellsing Ultimate: Volumes 1-4 Blu-ray/DVD($29.96 pre-discount)
High School DxD New: The Series Blu-ray/DVD($43.06 pre-discount)
High School DxD Born Season 3
Lord Marksman and Vanadis Blu-ray/DVD($37.39 pre-discount)
My Hero Academia Season 1 Blu-ray/DVD($42.99 pre-discount)
My Hero Academia Season 2 Part 1 Blu-ray/DVD($50.31 pre-discount)
One Punch Man
Ouran High School Host Club Blu-ray/DVD($30.72 pre-discount)
RWBY Volumes 3, 4
Serial Experiments: Lain Complete Series Blu-ray/DVD($22.99 pre-discount)
Shakugan no Shana Season 2 S.A.V.E Edition
Soul Eater Complete Series Blu-ray/DVD($29.96 pre-discount)
Speed Racer Complete Series Blu-ray($19.96 pre-discount)
Steins;gate Complete Series Blu-ray/DVD($24.22 pre-discount)
Tenchi Muyo: OVA Series
Devil May Cry Complete Series S.A.V.E. Edition
The Melancholy of Haruhi Suzumiya Seasons 1 +2 Blu-ray($40.00 pre-discount)
Tokyo Ghoul Complete Series Blu-ray/DVD($42.99 pre-discount)
Yu Yu Hakusho Seasons 2, 3
Only Yesterday Blu-ray/DVD($19.96 pre-discount)
Pom Poko Blu-ray/DVD($15.96 pre-discount)
Tales from Earthsea Blu-ray/DVD($14.99 pre-discount)
The Red Turtle Blu-ray($15.49 pre-discount)
When Marnie Was There Blu-ray/DVD($15.99 pre-discount)
Digimon Adventure Tri.: Confession
Dragon Ball Z Seasons 4, 6, 8
Dragon Ball Z Kai Seasons 1, 2, 3, 4
Dragon Ball Z Kai: The Final Chapters Parts 1, 2
Dragon Ball Z: Android 13/Bojack Unbound
Dragon Ball Z: Fusion Reborn/Wrath of the Dragon
Dragon Ball Z Double Feature: Tree of Might/Lord Slug
Dragon Ball Z: Broly Triple Feature($21.49 pre-discount)
Dragon Ball Z Double Feature: The History of Trunks/Bardock Blu-ray($21.49 pre-discount)
Inuyasha The Movie The Complete Collection
Naruto the Movie: The Last Blu-ray/DVD($14.99 pre-discount)
Pokemon: The Movies 1-3 Steelbook Collection($19.99 pre-discount)
This isnt an answer to your question, but I personally own the first blu ray set and do not recommend it. I use it but to play in the SD option. The blu ray/HD option ads very thick black boarders around characters and anything else that's animated making it stand out far more than it needs to in a very annoying aspect. Imo it IS worth it to get the blu ray discs but not play it in HD.
But here is the link for Amazon for the full season. https://www.amazon.com/Attack-Titan-Complete-Season-Blu-ray/dp/B01NCB8380
Desided to add the link so disregard the first part of the first sentence.