Your sentence is just fine. Expense or expenditure would work in the sentence. While the two words mean different things, either works and many people use them interchangeably, especially if they are talking about personal (as opposed to business) situations. While some other words could go in the sentence, expense or expenditure are the best choice. To be clear, here are "simple" definitions of the two words: Expenditure - any item that requires you to spend money Expense - any item that is a payment for a service rendered or "perishable" item received. So what is the real difference?? If you buy a house or a car, you have an EXPENDITURE BUT NO EXPENSE since you have purchased an asset that has a relatively long life. If you pay your electric bill for that house, or put gasoline/petrol in the car, you have an EXPENDITURE WHICH IS AN EXPENSE. As your car begins to wear out due to you using it, you have an EXPENSE BUT NO EXPENDITURE (this is because the car lost value that it will not get back and sooner or later you will have to replace the car). I hope I didn't totally confuse you!!

Yes, it's fine. I am curious to what you are trying to say, though. When his expenses rise, he usually has to borrow money from friends. "Expenditure" needs to be defined. Expenditure of what?

Expense

Either word can be used correctly here.

When there is a big expense, he usually has to borrow money from friends.