Trade Advice Needed

I am in a Full PPR league with 3 WR 2 RB 1 Flex 1 TE 1 QB and 1 Def. I feel a little weak at RB after week 1. I had Demarco Murray and Crowell as my starters. So I’m looking to trade for Fournette. Would I be over paying if I offer Golden Tate and Jonathan Stewart? What would be over paying for Fournette?

Line-up - QB Roethlisberger; RB’s Perkins, Stewart, Murray and Crowell; WR’s Tate, Jordy Nelson, Demaryius Thomas Fitzgerald, Doctson, Gabriel, Zay Jones; TE Ebron and Kittle; Def Rams