When I broke my electronic key (a Reanault Clio) a few years ago (about eight, actually), I went to the local renault dealership and they had to take the metal key part form the old one and put it into a new fob, which they then had to programme for my car, all for the princely sum of 130 quid When they quoted me the price I asked for a simple plastic one that I could just use as a key and do away with the central locking, but they said that they no longer made those or something.
With hindsight, going to the Renault dealer was a mistake, as they're always more expensive. A quick Google search for "replacement electronic car keys turned up a few places that do it, like this place in Southport, so I guess it won't be to hard to find somewhere near you that offers a similar service at lower prices than your local Peugeot dealership would.
I hope you manage to get it sorted without getting stung for too much!