Out elementary has one. They hold it in the school parking lot and charge by the parking space. Most of the revenue is from selling space and maybe concessions.
One of the real successful ideas is arranging for a Salvation Army or Goodwill truck in advance. They bring it the night before and park it furtherst back in the parking lot so it's the last item. If the PTO has a stall, it's just before the truck.
So as people close up - if they leave early, they can choose to donate their unsold items to the PTO stall. At the end, anyone who doesn't want to haul stuff home can put it in the truck and take the donations. It's really good because the PTO has no leftovers to deal with - even in their own stall.
We have a mom2mom sale twice a year! We sell tables for $17.00 for 1 or $30.00 for 2, we also have concessions for sale during the event. We advertise it and promote it through the school before hand. We do quite well.
This allows moms with kids clothing, toys they've outgrown, books, etc to be resold at an inexpensive price, while clearing out their houses. We also allow vendors to rent tables as well.
We charge $1.00 to buyers to come shop... We can make on average $2-3, 000 at each sale. This of course is after we pay our janitor fees since we have our sale on SAturdays-- But a great event every year.
I love this idea. It's all good. The school makes money, parents get to clean out their homes, parent save money on buying used items instead of new and all the stuff stays out of landfills. Economic, philantropic and green. It's perfect.
We have done events like you are planning but the chairpeople were not as organized as they should have been so the events didn't really succeed. I always wanted to do it on a grand scale: get donated warehouse space, collect donations all year etc. but I can't do it alone and couldn't find anyone in town to buy into the idea.
My girlfriend did this in Houston. She raised $86,000 for her childrens school. It took her all year to plan but the rewards were extraordinary.
I am sure you didn't have anything of this scale in mind but the potential is there.