I know it is standard practice in at least the good schools (~top 20) to pay for you to come visit, including airfare, hotel, and a dinner. I don't know if this is for international students also though. Usually the information for reserving a spot to visit comes in the same letter or slightly later than your offer of admission. It is an event for admitted students.
Looks like UVa doesn't pay for international students:
"If you don’t have a chance to visit on your own, we invite all the domestic applicants that we admit to come visit at our expense, typically in March. Further details will be provided with your admission information. Unfortunately, we cannot generally extend this offer to overseas students."
So perhaps it's not a standard practice to pay for intl students.