Once it hits 5 oclock, flea markets are gone. If there is some kind of night life, it is all under wraps by 9 PM. So, I would do the indoor small space and embrase the idea it is for every kid that comes to the flea market for $3. Adults sort of demand expensive facades, large buildings of mystery and something worth $20.
I have a hunch it could be actually somewhat successful. At our area tradedays there is a billy the Kid museum for $3 and some strange 800 SF pet a donkey and go in a mine and pan for gold attraction for $3 and the latter is always swamped. It is an interactive kid activity and one can only imagine that little kids go through basically two rooms of gold glitter on the walls and see a mine cart and a skeleton and all the parents know is they have a smile on thier face. Instead of buying junk, they got something for the day.
Really shouldn't be a problem with the fire marshal as the size is possibly below 1000 SF and it is only open a short time. So some stupid city permit for $45 might be in order or the flea market land lord is the god on this private property. You can be open and torn down and the land lord said it was fine. And it's for the children you smuck!
Of course in the real world, I judge success as making more than a job at Walmart making $62.50 for a days work and I have no idea what the traffic is there but the one here I'm sure could make $300 even on a bad weather day. On a good day it might be $900 a day. You can have a $150,000 haunt and still not put that much in your pocket.
I would go nuts with such an opportunity and convert it to Santas village and then for the summer maybe a haunted gold mine, all year once a month or what ever the flea market schedule is. Smaller is easier to convert to something else very affordable. So just being a goof just turned into making $10,000 a year.
The trick then over time is renvesting that money in storage costs and maybe even some animatronix whereas you know you are a success when the adults are paying $3 to see what the kids are so excited about. Take over the space and pay some marginal rent and lose the storage building. Some day that space will be the storage building for the haunt event you have on the outdoor property that is huge and has adults "trained" to come see it.
Another fabulous post from the U.S.Department of Wild Imaginings, now in spectaclar stereo, sponsored by the Adhesives and Sealants Council, suggesting ways to stick things together since the 1800s. Not fabulous in a gay way. Your results may vary. Illinois residents add 8% sales tax. These posts have been made by professional post makers, do not try this type of posting on your own without extensive training, lovely assistants and a trusty clown horn.