coefficient of friction may not be the appropriate metric here-- it usually refers to coulomb friction, which is linear in velocity, yet for drag stuff, usually the relevant factors are higher order in velocity. Fluid dynamics is frequently plagued with horrible nonlinearities.
I'm not sure where conservation of energy comes in, either-- clearly, when jetting, the squid is expending energy in the mantle constriction, so it's not a constant-energy system. I'm pretty sure it's spending energy in sucking water in, too.
My gut feeling is that energy alone is not the best way to look at this; I think understanding the momentum transfer of the intake and jet output of the water explains the gross behavior pretty well-- when the squid sucks in water, although it comes a bit more from the head than the mantle end, it's diffuse and comes in a wide aperture in a ring shape, so the change to the squid's momentum will be a little in the head direction (moving "backwards"). When jetting/exhaling, the mass of the water is ejected at higher velocity in a straight line directed by the funnel, pushing the squid forward. The mass of water is the same, but the velocity is both higher and much more directed.