I'd reckon 80-100 mill would be enough if Eriksen is dead set on leaving Spurs this summer. While he is their star player along with Kane and Alli he also has only 2 years of contract left. They would sell for a lot less next summer. Max 60 million, if that. Maybe they'll take the loss with the hope that they can do some damage this year in PL and CL. Not sure they have any chances in the league with City consolidating even more. So they will hope they can go deep in the CL which is easier but also pretty unlikely.
I'm dead certain that if Griezmann continues with Atleti, we'll set our sights on Eriksen until the 9th of August when PL closes shop for transfers. If that is good planing, I don't know.