This is a very simple app. No colourful design. very basic app. This is the flow I propose
a. on opening up the app - you will have a menu button - new vacation budget, my vacation expenses.
b. on clicking new vacation budget, the app will ask for name of the vacation, target amount, % of expenses towards categories. Here the categories are fixed in the app like food/travel/lodge/tourist attraction/shopping.
c. on clicking the my vacation expenses, it will display all the vacations. on choosing the vacation - you can enter the expense amt, date, category. on save - it will check it against the budget set - if within it will save, otherwise it will ask you to override.
d. there will be report button, which will give you the list like vacation budget amt and against each category the budget, actuals, variance. and the total.
thats all.
I shall do it in phonegap/html5/css.
I shall use testflightapp to deliver the test version to your iphone.
on your okay - we can submit to app store
all the icons/screenshots have to be provided by you for the app store submission.
regards
Prem