I've been wondering about this too - I'm particularly clueless, as the Tooth Fairy brought me five pence a tooth when I was little (mind, three years previously, the same coin would have been a shilling). I guessed a pound would probably be the going rate, more or less, and am saving a particularly shiny one just in case. Have you noticed that in the Charlie and Lola episode 'My wobbly tooth must not ever never come out' Lola and Lotta never mention how much money the Tooth Fairy brought: they just get 'a coin'?