She started her business 'on a small/tight/shoestring budget' [=she did not have much money when she started her business] and could not afford to overspend.
The government may have to raise taxes to 'balance the budget'. [=to have enough money to provide the amount that is being spent]
The project was completed on schedule and 'under budget'. [=it was completed for less money than had been planned]
(..) you haven't lost your sense of humor. Even if you have lost... most o' my money. Actually, you did that. If you funnel your entire R & D budget into a fusion project that you then mothball, - your company is unlikely to thrive. - What are my options? Well, if you're unwilling (..)2012 The Dark Knight Rises