That's a last generation Roubaix frame, and unless you're getting the storage box, same fact 10r carbon as the Comp level. A bunch of us on BF got in on the sale they had on Comp Di2 Roubaixes before the intro of the current gen for less than the MSRP of the Expert non-Di2 Ultegra. So I would guess if you're selling it without the wheelset and drivetrain, maybe $1K? I like my Roubaix, but it's not anywhere as sought after as a last-gen Tarmac (SL6) or Venge frame, so whatever those are going for would be a generous upper-limit.