As far as Tapsoba is concerned, I think Leverkusen will say it's 55mil and not a penny less...and that's before we even get to bonuses. They know what they've got and that if he had another big season for them, he'd either stay to play CL football or go to Bayern/City/Real/PSG for 80+.
I just don't see us spend that kind of money, not when we've got such a bloated squad. If we somehow managed to get a few mil for Sanchez, Dier, GLC & co, then yeah perhaps. But I'd be stunned if we invested big on him or another CB before we shift some deadwood.
More likely we'll get one or 2 backup type dudes first, then have a pop at Tap later on if the stars align.