Since the descipting say's: The spell uses the slot level, spell save DC, spell attack bonus, and spellcasting ability of the original caster but is otherwise treated as if you cast the spell.

would the HP of arcane/bigby's hand be equal to the one who stored the spell, or the one casting it from the ring?

Quote from GeraltvonTrivia >>

Since the descipting say's: The spell uses the slot level, spell save DC, spell attack bonus, and spellcasting ability of the original caster but is otherwise treated as if you cast the spell.

would the HP of arcane/bigby's hand be equal to the one who stored the spell, or the one casting it from the ring?

 There's a reasonable argument either way. I'd rule that the original caster sets everything about the spell. The ring stores the spell at the instant its effect is created, to be released later. That's just an opinion though. Check with your DM, or if you are a DM, choose whatever sounds most reasonable to you.

So you charge the ring then take a rest recover the spell slot used to charge the ring.

I know this is probably a big ask, but is it possible to make this item show what the PC or NPC has stored in it? A lot of people use dndbeyond as their character sheets now and having this shown would be peachy keen.

Where can I find the price?

I'll probably end up filling it up with shield or mage armor

Say I have a few wonder ranger in my party(or anyone who has an ability to cast a spell without requiring concentration) if they cast the spell into the ring and choose for it to not need to be concentrated on(and thus shorten the duration) would the one who casts if from the ring also gain said benefit of not needing concentration on that casting of the spell?

This is a Rules as Written verse Rules as Intended question. "This ring stores spells cast into it, holding them until the attuned wearer uses them." + "Any creature can cast a spell of level 1 through 5 into the ring by touching the ring as the spell is cast."

My player has used this while grappling a wizard and argued it should store the spell the wizard cast if it's able. Technically he is right as the ring's effect requires the caster to be touching the ring while casting a spell through 1 to 5 for it to be stored. BUT it's also intended by the first sentence that the caster be a willing participant to store the spell however the explanation doesn't actually say that at all. I'm in a quandary on which way I should rule for this for future rulings. On the fly I allowed it but did state I'd look into it as it's RAW verse RAI. Thoughts?

Just getting in before someone says it, no, the ring doesn't require the person who gets their spell stored to be attuned, only the one who uses the ring to cast the stored spells.