Building a new one would cost a couple of billion in development costs, but being the optimist, I think £120m would get her airborne again. After the AF disaster a lot of modifications were made and the air-frames have nowhere near reached their full life cycles.
Likewise the engines, assuming they are still around, will likely still be in good condition though obviously maintenance would be needed.
I don’t know about the avionics and over the last 12 years they’ve obviously become more sophisticated, but there are still many aircraft flying with older avionics than are fitted to Concorde, so with some modernisation will be fine.
All in all I wish them luck and look forward to what would be my third Concorde flight!