The peg only says: "1 PRL will grant you X GB/year of storage" - Nothing more. X is independent of the market value of PRL.
Means with the starting peg of 64GB/year - it is totally insignificant what current price PRL is on the market or at which price you bought it - you will always get this amount of storage.
This implies that the price will drive to an equilibrium - since you have a measurable countervalue in storage. Nobody wants to buy overpriced storage, nobody want to sell undervalued. This whole supply&demand is nothing else with every other currency, but you have a fixed countervalue in storage and that is what changes it all.
E.g. look at Tether (It's not that easy with PRL, but it should give you an understanding of the peg):
You would buy my one tether for 0.5$, because you know it has a countervalue of 1$. You wouldn't buy my tether for 1.5$, because of the countervalue of 1$.
So both parties (buyers/sellers) meet in the middle for the actual value, the equilibrium.
As I said, it's not that easy since it isn't that easy to determine the value of 64GB/year of storage by a single person in comparison to 1 USDT = 1$, but with this I try to give you an understanding on how an equilibrium price-wise will eventually be achieved.
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1) If more people are buying PRLs, more people will use PRLs for uploads.
2) More PRLs are getting buried for uploads in datamaps means web nodes (website visitors) can find more PRLs in datamaps. (in total, not individual)
3) More website visitors finding PRLs will lead to more website creators receiving more PRLs
4) Website owner now can hold the PRLs, use them for own uploads OR sell them for revenue on the market, since they need to pay bills themselves afterall
5) Cycle continues.
This is how stability is created - through a closed ecosystem where the PRLs are constantly changing from "Storage user" -> "Buried" -> "Website owner" -> "Storage user" -> (...)
Basically it will be a continous exchange between people selling PRLs off for revenue and people buying PRLs for storage.
=> So we are still driving towards an equilibrium.
Source:
https://www.reddit.com/r/Oyster/comments/8fouax/can_someone_please_explain_how_the_storage_peg/