Simple app suggestions for recording and dividing payments?

My Dad is looking for a simple app that can record payments and then divide them (he is going on holiday with some friends and wants to keep tabs on things so they can split everything equally at the end).

I thought the obvious suggestions were Microsoft Office but that's only available on iOS 7 (he's still on iOS 6) or Apple Numbers but that is a fair bit of money.

I'd live to hear any suggestions for apps that might be for for purpose (doesn't need to be a spreadsheet app if there's something simpler)