He's the next great striking hope and Red Bull have been gearing up to sell him a fortune for years now so I don't see how you get him cheap, especially when they could keep him for another maturation cycle in the hope of even more money next summer.It will be interesting to see how much Sesko actually costs (if the deal actually does happen), as there's reports Leipzig are hoping for close to €90M, but there were reports coming out for a couple of Arsenal journalists a few days ago that taking into account transfer fee, wages and agent fees Sesko would work out slightly cheaper when there was comparisons of the 2.
He's an extremely talented young player but has a lot of things yet to come together in his game, but I doubt that gives you any leverage in negotiations as above, Leipzig won't have qualms about keeping him another season.
Of course, you're moving in for him before a potential breakout season, which once/if he has, the current price will be seen as derisory.
I'll be very surprised if you get him for less than Gyökeres as an all inclusive package. If Sesko is the golden goose, why would he or his people accept less in wage and fees than Gyökeres? I'd be very surprised if they're not on a similar wage if they both come to the PL this summer.