The OP needs to provide more info, as this can be radically different depending on the flight she / he wants to book. Is it an inter-european flight? Or a direct long-haul flight from FRA or ZRH? Or starting e.g. in MXP, and connecting through one of the hubs? etc. etc.
I'm a bit surprised by the response from Chris63. In my experience one can save quite a bit, especially on long-haul flights that depart from ZRH, e.g. ZRH-NRT are often very expensive to buy in C directly. It also depends if the OP has any status. I've been successful as SEN with most of my bids, using the lowest possible bid (or just 10 CHF / EUR more than that)
Also: in some cases, it's acceptable to have one leg in eco, but the other leg must be in C. Booking such a combination works much better with bidding.