For those who are timid about buying tickets on eBay, may I suggest another course of action? Sell on eBay! Especially if you have a good feedback rating.
There are plenty of people willing to buy partially used tickets, especially if you price them cheap and use Buy It Now. If you get multi-day tickets and use just one day, you're effectively using the cheapest day on the ticket and you can sell the rest.
I suggest looking at eBay and seeing what partially used tickets sell for compared to your needs. I've done this before, and ended up paying less than $20 per person per day.
Another point: if you are only going for one day, you can't hop unless you buy a multi-day pass.