If the corn maze will honestly be in a cornfield, then why not stick with a fear on the farm type of theme? I always pick my theme, then list characters, then list sets. Then I have to pick the best, or the easiest/cheapest to do. For a fear on the farm theme I would.....
moonshine making mutants
inbred hillbillies (think last house on left)
children of the corn
jack o lantern headed scarecrows
Pumpkinhead (movie had a very rural setting)
old swamp witch
cannibal family (resorted to it after years of drought)
Minotaur (half man half bull)
zombies (they fit in almost anywhere)
chainsaw maniacs (fits in with in-breds and cannibals)
country graveyard (wooden crosses sort of thing, not victorian)
animal pens/slaughter area
chainsaw mans shack with body part freezer
um...cornfield (crow sound track)
burned out/down farmhouse (opens up options for rooms)
scary ass barn
woodchipper/mulcher used for people (could have a spitter in it)
hanging tree (dozen bodies or so hung from same cool looking tree)
Tractor scare area (like the classic train scare)
these kinds of excrcises (listing of sets and characters) allow me to focus my vision on exactly what I want to accomplish and see, I would see what characters work together and then what scenes would work and flow best from one to the other. Using your space with as little alteration as possible will help your budget. A clown theme will have to work twice as hard and be twice as detailed to be believable in a cornfield setting, the same with an asylum theme. first year use what you have and give a quality show, then you can add a nearby asylum or circus into your theme and add a few of those elements into your attraction and back story.
Regardless of which way you go I see alot of shredded flannel shirts in your future.