Been going to GenCon for many many years. We have never stayed downtown. Usually, by the time we get into housing "lottery" of some sort, everything is sold out and we have to book 30 minutes outside the city. There was only one year we have ever used the housing block to book and that hotel wasn't downtown. This year is the first year I haven't been able to book a room outside the block that isn't 45 mins+ outside of Indy. I don't know what's gotta give but something has to.
This has to be your budget/choice of hotels that you are 45 minutes away not availability. There are plenty of hotels still available within 30 minutes of downtown for around $100 a night such as the Country Inn in Greenfield ($103) and Baymont Inn NE($85), Baymont Inn Fishers ($105), and Suburban Extended Stay Northside ($85).