Offer them what you think the fittings are worth - and get a quantity for the logs left. I've just moved back from abroad and sold lots of things at real 'knock-down' prices just to save me the trouble of disposing or transporting them. E.g. Cooker 25 euros, 2 settees 75 euros, washing machine 30 euros.... etc.. Cross-channel removals come expensive and they have a time constraint.
In other words, don't offer them a lot. Don't know what sort of cooker it is, is it worth your while to offer £100? Only you know the answer. Bonne chance!