Yeah, I don't think Ted Thompson will trade for anyone that costs him draft picks or starters. He just doesn't work that way. Aside from Charles Woodson, I don't think anyone of note has been acquired from another team or through free agency.
I still think Seattle makes the most sense, especially after not getting VJax (so far). Also New England often surprises by making moves like that.
However, I think it is equally as likely they just keep him in Buffalo. You don't become the modern Buffalo Bills by making decisions that actually benefit your team - unless they figure out a way to play all 4 RBs at the same time, they are killing themselves right now. Perfect opportunity to use valuable players at a position of depth to rebuild talent on the rest of your roster, but they'll probably botch it up like they always do.