Keeper trade for picks value

I play in a PPR redraft league where we can keep one rostered player. No pick is associated so it’s not like if you drafted them first round last season you lose your first round pick if you keep them.

That being said, how do would you go about valuing a keeper trade? By keeper trade I mean someone has a roster of multiple “keepers” and they are better than my current potential rostered keepers. They want picks in return. If you were to say trade for JJ or someone like Jamar Chase, how would you personally determine the pick(s) that go to the other team?