Chain shirt +3 is 2,000. Elven Chain is 5,000. No idea what the difference would be but traditionally, Elven Chain is not +3 to AC. Is the 3,000 gp difference just because of rarity even though both items are listed as "rare"?
Well, Elven Chain is +1 AC, but also grants proficiency with medium armor when worn, which is huge for mage classes without armor proficiencies.
For a fighter, Elven Chain is worthless compared to a Chain Shirt +3, but to a Sorcerer the Chain Shirt +3 isn't even a possible option, while the Elven Shirt is. Sure, it's only barely better than Mage Armor, but it's a spell you don't need to know (if a Sorcerer), and a spell slot you don't need to expend (for any magic user that depends on that for AC), while still being an improvement.
If you spot anything out of whack, please do let us know.
On the giant strength stuff, you have a "Belt of fire giant strength", but no potion of fire giant strength. All the rest have pairs of belts and potions.
Also, you'll want to tidy up whether you uniquely list frost and stone giant items (as you do for the potions), or combine them into a single entry (as you do with the belts).
Same with the potions of Giant Strength. Is a potion of storm giant strength really 45,000 gp "better" than a potion of cloud giant strength?
Earliest able to afford*:
Potion of Giant Strength (hill giant) (300 GP): 2nd level
Potion of Giant Strength (stone giant) (800 GP): 3rd level
Potion of Giant Strength (fire giant) (??? GP): 5th? level (maybe 2000 GP)
Potion of Giant Strength (cloud giant) (5000 GP): 7th level
Potion of Giant Strength (storm giant) (50000 GP): 15th level
Note*: For affordable, I'm using the table
@Morrus provided, and picking the first level where the starting + gained wealth total is greater than the item cost.
The Potion of storm giant strength is out of scale with the rest of the potions. The others scale up in cost to be affordable (if only just) about every other level (2, 3, 5, 7). However there's then an 8 level jump before the next one is affordable.
What seems more appropriate for the affordability ladder would be a price of approximately 10,000 GP. That would make it possible to buy at 9th level. At worst, 20,000 GP to put it at 11th level on the ladder.
Earliest able to afford ten*:
Potion of Giant Strength (hill giant) (3000 GP): 6th level
Potion of Giant Strength (stone giant) (8000 GP): 8th level
Potion of Giant Strength (fire giant) (??? GP): 11th? level (maybe 20000 GP)
Potion of Giant Strength (cloud giant) (50000 GP): 15th level
Potion of Giant Strength (storm giant) (100000–500000 GP): 17th level – never
Note*: Same affordability metric as above, but being able to afford 10 means being able to casually make use of the potion, rather than it being most of your total wealth just to have a single one.
Scaling isn't quite as neat with this one, but at 10,000 GP per storm giant potion, you can buy up 10 at 17th level, whereas at 50,000 GP per potion you will never have enough wealth to buy up 10.
Given that the cost of a belt of equivalent giant strength (of any type) is very roughly equal to 10 potions, it confirms that the storm giant potion is out of scale with the rest of the comparable items, but that a 10,000 GP price would be entirely appropriate.