Here's my idea for selling tickets: On Wednesday nights, have someone from the ticketing department head to Party in The Park on Yeatman's Cove with a roll of $5 tickets and a roll of $10 tickets. I'd bet they'd sell at least a couple of hundred. You've got a couple of thousand people with disposable income within an easy walk of GAPB.
But I agree with a couple of the posters -- you can do Great American relatively cheaply.
But the only marketing strategy that works consistently in Cincinnati is winning. Just look at the Bengals, UC and XU. When the Reds put together a winning season, they won't need 4 for $48 to break 20,000 in attendance.