'a prey' is incorrect.
It is not a singular noun by itelf.

It would be 'a prey animal'.

'Prey' is uncountable - the concept of what it is that you hunt and eat.

Therefore it does work with 'its prey' = the thing that it is trying to catch/has just caught.

A predator can search for, select, pursue and kill its prey (another animal). After it has made a kill, why can't the predator eat (devour) its prey? After the killing, its prey is its kill.

2 isn’t unnatural many people would use “its prey” rather than “its kill”, they can be treated in this context as synonyms.

(2) is OK as Sarrriesfan pointed out. - Their actions were in comparison, with emphasis on amount, speed.
(3) is grammatical, also acceptable. - Jack (eating ...) was like a hungry wolf ..., also suggesting the way (e.g. very messy) they ate.

By "a native AE speaker", you don't mean a descendant of north American aboriginals?

Thanks, Write Edge.

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When I first read the above post a few days ago, I couldn’t help feeling something blowing in my face - it’s the air of authority from the comment! I wasn't sure that I wanted to spend more time on this thread. Now a prank by the same poster’s https://forum.thefreedictionary.com/postst207930_Which-is-correct-.aspx
brought me back and I thought I may as well say a few words.

The sentence "Jack ate his steak ravenously, like a hungry wolf devouring its prey."
has serious problems. First, how would you feel if Jack is your friend, a family member, or indeed yourself? Second, the sentence suggests “a wolf devouring its prey” is a familiar sight but in reality, they usually share their prey, typically a large ungulate like a deer. (Strictly speaking congruence requires Jack ate a cow raw.) Third, it’s a "good" example of pleonasm. You see on words like “ravenously”, “hungry” or “devouring” in the phrase “eat like a pig” yet it conveys the intended meaning with precision.

In a precious post I said Sentence (2) is slightly better as it sounds a bit less personal because of its structure and length, and “would” signifies that “a single wolf devouring” is an imagined scene. People discuss grammar on this forum; Sensitivity is not an issue. Now because Jack’s steak had a fixed size, the focus must be on his table manner. Therefore, I'd suggest: "Jack ate his steak like a wild dog."