I just want to repeat this. Many seem fixated on what the home owner is providing for the event, but the answer is "nothing". They're not providing the tables, chairs, tablecloths, cleaning, or food/drink... all of which normal wedding event locations provide and factor into their cost.
If I normally rent a VRBO house that sleeps 15, but only bring two people for $300 a night, and then one year bring 12 others, I'd still expect to pay $300/night. Or, I have the house that sleeps 15, only bring 2, but have a party (presumably allowed) that brings a dozen more, I wouldn't expect to pay more. What's the difference?