Rejecting work which does not compensate for our efforts is the naturally logical thing to do, it is still mutually exclusive to what happens to the final work after it is delivered (or whether it gets resold at a higher rate). Reselling has nothing to do with us freelancers demanding the remuneration that we deserve. It’s a completely orthogonal issue.
If you are not being paid what your work deserves, then that is one issue. (It needs to be resolved on its own merits)
If some sub-contractor is being paid more for doing the same, then that is a separate issue. (I still insist that he is not being paid ‘for the same work’. He is being rewarded for hustling and bringing in the sales)
Almost none of my gigs use ‘gig packages’, and almost none of my sales are below 35$ per gig. If the work was not worth what I demand, they would be paying 5$ to someone else. As long as I am paid what I think it is worth, I do not bother whether they resell it or use it for themselves. Some of my clients have indeed been web development agencies, but I never bother myself over how much they might be making off my code. I get paid what I ask, I get raving reviews, and the same buyer comes back again for repeat sales. I am only 2 months old, I have only 25 sales to my name and already received tips from 4 people who have become repeat customers after falling in love with the value that I offer. So, here is a case of someone paying more than what I asked.
I don’t know why the sub-contractor revealed how much they were being paid for the gig by their buyer, instead of simply working out an arrangement which is acceptable to both of you and has nothing to do with the other buyer. If you negotiate well and make a value proposition which you are confident no other seller would be able to match, you can always command higher prices. Everyone has their USP, just find yours and wear it like a badge. I am mindful of the fact that all a buyer needs to do if they find my quote too high is to use the search bar to find someone else to do it for 5$, but the fact that no one on Fiverr does complicated programming projects makes them see value in my proposition. Make a value proposition and raise your prices, as @emmaki always keeps saying.
Or, you could hustle and justify the value that you offer.