Here's a few things I found:
Namor the First Mutant two collections are $2 and $4
https://www.comixology.com/search/it...pe=COLLECTIONS
Both John Byrne collections are 6 bucks each.
https://www.comixology.com/search/it...pe=COLLECTIONS
All 8 Marvel Masterworks Sub-Mariner are on sale for 5.99 a piece! That's the entire Silver / Bronze run of Subby. They are like 50 to 75 each in print. And the 3 Golden Age Marvel Masterworks are only 2 bucks each.
https://www.comixology.com/search/it...pe=COLLECTIONS
The 3 Golden Age Human Torch Masterworks are also 2 bucks each. The infamous Namor / Torch battle with the flooding of the entire world is in the second on of these. There is a Subby story in each individual issue, so there's a few in a each book.
https://www.comixology.com/search/it...pe=COLLECTIONS
All 7 of the Golden Age Marvel Comics Masterworks are also 2 bucks each.
https://www.comixology.com/search/it...pe=COLLECTIONS