I recently went to Halloween Horror Nights (google it).
One of the haunted houses was set up like so
every room was separated by thick black plastic sheets you could spread away, almost exactly like the clear plastic sheets found on loading docks only solid black. That way you can't see into the next room. the scariest room was pitch black, huge, and had about 20 zombies in it, and a strobe light that went off every 10 seconds or so as your only light source the zombies would brush up against you and all turn towards you as you entered the room (they were all actors, not animatronics) EDIT: and you had to find your way out of that room by the way, there wasn't a clear exit out of there... >_<
you'd go down some pitch black hallways where theres nothing set up, but some black streamers hung from the ceiling at head level, so as you're feeling around the hallway you hit your head on the streamers and in your paranoid state it feels like several people trying to grab you from above, only hitting you with their fingertips. Another cool thing was a hallway just as before but it had one of those little spring arms at chest level (padded, not just bare spring) that as you walked through it feels like someone is clawing at your chest.
There were alot of hidden corners in the shadows where people would hide and pop out just after you pass them so you see them lunge at you in the corner of your eye.
One thing that was cool that I doubt is in your budget was a narrow hallway, pitch black (again, I know) but they had an inflatable cylinder taking up a larger portion of the hallway so you have to push through to a very tiny space, in order to pass through, it gives you claustrophobia even if you don't have it >_<
I know it doesn't really fit what you're after but it was scary as hell none the less...
this was at the asylum, but there were two airbags.
it was creepy as hell because our group stopped in the middle. >_<
well, I think we were gonna have a hallway about 20" to about 2' high.
"There were alot of hidden corners in the shadows where people would hide and pop out just after you pass them so you see them lunge at you in the corner of your eye."
this is going to be most of the haunt, even though there will be a "bug hallway" someone is going to bang on the wall and scream "DON'T STEP ON MY FRIENDS! THEY ARE THE ONLY ONES I HAVE!" but when you walk in, there will be a strobe going off. you will feel popping under your feet, and in reality, they will be rubber/plastic cockroaches. they will be all over the walls, the ceiling, the floor, everywhere.
UPDATE!!1!1 this halloween, i am going to make a "stalkaround" costume. these are much like puppets, but are about, oh, seven feet tall or so. afterward, i will make more if possible, and they will be the centerpiece of the outside of the haunt. they will be dressed up in straitjackets if possible, and there will be one inside who will chase our victims.