Sorry, wasn't sure where to post.

I'd really like to rent a car for my trip tomorrow, but given I pick up tomorrow and drop Friday, the rate is nearly $300. If I pick up tomorrow and drop Saturday, the rate goes down to $100. What happens if I reserve the weekly rate and drop a day early? Do they switch me back to the daily rate? Please help if you can--I'm anxious to get this taken care of. Thanks!