Ok, this number worked. Here is the deal for sites with electrical and water. You cannot reserve one of these sites until June 28th. But you can reserve a site over the phone beginning on that date. This is different than than the process of staking out a site without electricity starting June 28th. You have to be present in Oskhosh to stake out a site without electricity.
If you reserve a site on the phone after June 28th you begin to pay $55/day for the site whether it is used or not. You pay until August 4th. So if you are willing to pay the price you can have a nicely located site with electricity and water waiting for on opening day of AirVenture. So going that route you are basically paying $300/day for a reserved site for the duration of the event.