Well, we already know that MS is more willing to lose money than Sony at this point and will spare no expense as opposed to Sony who isn't trying to lose too much from the SSD. Here's my prediction:
XSS: $249
XSX: $449
PS5 DE: $449
PS5: $599
It's the only thing that makes sense.
I have some good news, and some bad news for you ;-)
You will be able to get your PS5 for a little less than that, but your XSX could cost considerably more.
I don't think we should ever frame the question on retail price as if the key consideration is what your chief rival is doing - both are huge businesses with responsibilities to share holders, first and foremost. Adhering to internal sales and profit budgets will be far more important than simply undercutting a rival.
In Sony's case, they have only failed to sell in excess of 100m units once (for a home console) and, I think its fair to say, they prefer that scenario to "only" selling c.85m! Cerny delivered a console (PS4) on time and on budget that has delivered more profit than even they could have ever imagined, after the money-sink the PS3 was.
Having trusted him again with PS5 do we really think the breif has changed and they will be forced to go up-to $599? For me, no, unless of course they just get greedy.
The PS5DE is primarily a response to how their customers are using the PS4 - it also happens to be an excellent way of locking people into the ecosystem and selling more PSN subscriptions.
The next stage is getting people to upgrade to PSN+. Hence why GoT : Legends is free with no MTX, they just want people to buy the game at full price and they subscribe to PSN+