Photobooths are around 500-700 for an evenings hire. What about setting up your own with props and someone willing to take pictures? You could get everyone to sign a guest book, then attach their photos on 'their' page as a nice keepsake for yourself.
You could set up a 'pub quiz' for during the meal. Each table answers a set of questions about you and your OH (you can give them a card to answer on during meal, as opposed to someone shouting out the questions) then the best man can mark them up at the end of meal, with a prize for the winning table?