Interesting how 'oil prices' drive costs in one direction only!
I think spicejetter is dead on, sit down and work on the numbers based on logbooks and bank/credit card statements. That's the only think that will hold water when making a complaint or trying to retrieve money from an FTO.
Always keep accurate records, buy a folder to keep everything together for example. I know from experience how frustrating it is to not be able to find that important document where debt/debtors are concerned!