Chicago venue for amateur open mic (9/26/15) - Any suggestions?

I am looking for a venue in Chicago to host an Amateur open mic event on September 26, 2015. This would be associated with a large water and wastewater conference (WEFTEC). Last year we did this as a fund-raiser in New Orleans at House of Blues and donated $17K to various water charities. The big name places in Chicago seem much steeper in pricing. Anyone with any suggestions? Most of the conference hotels are downtown, so the closer the better, but we're open. Looking to have around 400 people.

Old Town School of Folk Music? They have a good concert venue. If you're looking for a club environment, wouldn't suit you.

We're definitely looking for a club environment with a bar atmosphere. Thanks, though.

If you're looking for a club environment with a bar atmosphere, you need to look in the neighborhoods for most of your options.

Reggie's Rock Club
Logan Square Auditorium
The Hideout
Schuba's
Double Door
Beat Kitchen
FitzGerald's (in the near western suburb of Berwyn)
Wire (also in Berwyn)

Of course Chicago has its own House of Blues.

I've played Schuba's before. Very nice bar with a great stage.

Thanks for the list, Steve!