I was doing the same type of research when I needed space for a for profit venture. Here's what I found:
I'd suggest checking with nearby colleges and universities. I know there's a part of Duke that rents space out, but that may be a bit of a trek for some of your participants. Here's the info on Duke:
About - Sanford School of Public Policy - Facility Rental
Check local hotels for their rates. I believe the Wyndham Hotel and Holiday Inn Express both on Miami Blvd. (both in SE Durham, not too far from Brier Creek) was the one that was most reasonable.
There are the local Parks and Recreation facilities. I don't know about other places, but our recreation centers in Durham have rooms available (think parties and family reunion type rooms) year round for rental.
Another option are retirement communities. I only knew of one place in particular that did this and they were really picky about who rents their space.