Babysitting

Hi everyone,



I was just wondering how much people pay for babysitters? I have a friend who has started looking after my son on odd occasions who I want to pay something but I'm unsure how much to give her. She's coming to ours in a couple of weeks so I can go to my Christmas party and is going to stay over as she has work the next day so doesn't have to wait up for me, so how much should I pay her?