As a Petrean I'll give you as much information as I can.
First the boring facts:
Basically KFC is £119 at Peterhouse.
Unfortunately you are obliged to each a certain amount of dinners (not lunch or breakfast) a term. A dinner constitutes a min price of £1.90. You have 30 'signouts' a term at your discretion where you can decide not to turn up to hall. Any you don't use are carried over to the next term. If you go over your alloted signouts you get charged £3.50 per meal missed.
The apparent reason for this system is to ensure enough money is coming in to justify having formal hall every night and ensures everyone has regular social appearances.
Nevertheless it is an unfair system, one that we've been fighting to change. As yet College have offered us an alternative system involving a minimum spend across the term but we rejected it as being even worse.
There are a number of things you can do though
1)Opt out - they don't let you know about this a lot but you can opt out of the KFC and thus the obligation to turn up to dinner 4 times a week. However it does mean that you have to pay VAT on any meals (and formal hall ticket) which you don't normally have to pay. In addition college is not obliged to give you decent cooking facilities (and unless you're in WSB, the facilities are rubbish) unless you have a specific reason to opt out (and by this, college means religion or dietary requirements NOT veganism etc)
2)Use hall as a shop - The buttery sells lots of things other than hot food like crisps, chocolate, drinks even cereal boxes. Buying these counts as a 'meal' provided you spend at least £1.90
3)Cheat - Find a trustworthy friend who uses hall regularly and let them use your Peterhouse card to buy their meal and let them pay you back. You get a free signout, result! Of course you can't do this too much or you friend will lose their's
On a final note, even if you're a picky eater (like me) you may find that the buttery gives you enough options. Give it a go before you opt out or anything.
Hope that helps