Check for community centers (that route worked like a champ for us last year-really cheap compared to most other places), large churches, hotel conference rooms (gonna be much higher than the rest). In the best case, you want something with tile/linoleum flooring for spills, plenty of electrical outlets around the space for people to plug in, and easy access for peopole hauling large displays (hell, anything over 10g is a larger display if you have to walk very far

). We did the hotel conference room the first time (got it for about 1/4-1/3 the cost of what they wanted this year). That worked out great because they had an Applebees on site and plenty of parking with a few doors that lead directly to the parking lot (8 feet outside the door). Last year, the cost from the same hotel increased dramatically, so someone mentinoed the community center. When I saw it I figured it would work great. Outlets, linoleum flooring, and drive up access for unloading. Cost was really low in comparison to other options.
My plan was to never really make money for the club on frag swaps, but to break even. We've always made at least a couple hundred, though (having given donations from proceeds to a good cause).
Just setting the spot is a tough thing to do, but then the real work begins. You have to invite people and keep posting in other forums to draw attention. If you can get the newspaper to do an article sometime around the anticipated date, that helped us two years ago (and I got my 15 minutes of fame

). Sometimes radio stations will make announcements for NPO type clubs at low or no cost (we never got that one to pan out, though).
Sketching the room up-and people laugh at me and don't let me join in their reindeer games because I'm such a dork using ACAD, but it is a very useful tool to make sure you don't overpopulate the room and ensure there is plenty of room for people to move around, etc.
Then comes the need for sponsors and donations. I was lucky enough both years I set up the swaps to get a decent amount of donations from sponsors in a short amount of time (West TN had a bunch of donations in hand before the first one, so they threw those in, raising the pot). It is better if you can start asking early, though, so they can plan. Same for inviting companies like Just Coral, etc. They didn't make ours last year, but were at the first one I did and brought a lot of nice stuff.
Then there's the raffle... I did the setup by myself on the first one 100% and about 99% by myself on the second (had a lot of help on the second one on the day of the swap, though, thankfully). The whole process will stress you out, but when it turns out good, you are rewarded internally for the success. I always wanted the Tn clubs to get together and discuss options for frags swaps and arrange them around the year so people from different areas could hit one every couple of months, depending on how far they were willing to drive. Think of the diversity. We've had people from Wisconsin and Missouri come, as well as all surrounding states. Kinda helps build networking, too.