. . . we weren't going to have an 'official' photographer on our 2 hour party bus tour, as I was planning on asking a talented friend to help us out, but sadly she's not coming any more

So going on the glowing reviews B & W have had, I've taken the plunge and booked him - my ever growing budget's not happy, but I am!
So that I can work out exactly what to put in the budget for it, can I ask you guys what you would consider a decent tip for photography services for 2 hours?
Which reminds me, do we also need to tip the Cashman photographer who will be doing the ceremony, or is that not necessary?