While tickets don't go on sale for Paul McCartney's Summerfest show until next Friday, it's already top of mind for many.
TicketKing in Milwaukee said they've already gotten calls from people looking for tickets. They said if you don't get a seat when they go on sale, they price will probably be much more expensive. Ticketmaster lists the starting price around $75, at the high end just shy of $385.
TicketKing suggests trying to get your tickets through TicketMaster first, then turning to a reliable secondary seller.