Parable

hey, me and my film crew from school are making a movie about underground street fights (there is a story invovled int he movie) neways, we are having fighters (kickboxing, wrestling, boxers, kung-fu) and we are trying to figure out how to make a sort of ring for this? its like a fast and furious kinda thing but involving street fights...we were thinking of having cars in a circle pointing inwards...but thats hard to do without attracting attention...so if neone has ne ideas for a ring that isnt that expensive....give us a hand in some ideas?

thanks