It certainly is an interesting idea and one that we've been exploring for a while. As an FYI, I've got about 15 years experience in the entertainment end of fairs and have taken a show (not a haunt) to about every event in the US at some point or another so I've got a fairly good handle on how it operates. Not 'pooh-poohing' the idea at all, because it could be a good opportunity, but there are some things to consider depending on how deeply you want to get involved. Totally doable, just keep these things in mind as you develop your plan:
RATES: The most interesting thing (obstacle?) about this industry is there is essentially not an industry standard. Every single event you encounter will present you with a different business model. For vendors particularly, it's an extremely competitive environment and of course... depressingly, it's all about the money. Real estate is premium. Once you get accepted, some events will charge based on linear feet of your space, some will charge on total square feet of your space, some will charge a percentage of your gate, and then most will come up with some bizarre concoction of all of those formulas. Just be prepared with a calculator. **See below
TRANSPORTATION: If you're just considering doing a couple of local fairs in October, then this next part probably doesn't apply, but be sure to account for transportation costs of the trailers. If you don't have access to tractors, most companies will move trailers in the $2.50 per mile range (or less) and there are several good resources for that. But if you're just talking local and have a buddy with a truck, you could certainly strike a better deal.
INSURANCE: So far most events are still sticking with the standard $1M liability, but some events are pushing up to $2M and in some cases $5M. Ugh. But that hasn't been so widespread yet.
POWER: This is a real consideration. Attempt to keep your power needs to a minimum! Can't stress this enough. Our show required 100 amps and that was a huge struggle almost everywhere we went from quality of the power, to distance of cable needed to reach the source. Not to mention actual amps available and their reliability. A good strong quite genny would be great if you could pull it off. Not a deal breaker, just be very specific in your pre-show discussions.
LOCAL REGS: This one will make you crazy(er). Every county of course is different. I'd suggest going the extra mile on safety, then have overwhelming comprehensive safety documents for the attraction that you can
'wow' inspectors with. Too much is worth it... rather than a 'no' opening or incredibly expensive last minute runs to Home Depot. Keep in mind, that while some safety regs are seemingly more relaxed as a temporary installation, some (SOME) inspectors can be a little tougher on the fair industry as they can hold a bias that the 'gypsy' nature of the industry creates a greater risk. Lots of documentation, and a friendly and professional attitude will do wonders.
LODGING: If you're local, then no worries. Just be sure to figure in housing costs for your folks and per diem, etc. if you are going out of town. If you have access to RV's most fairs have a lot for just such a thing at a reasonable rate. Motel 6 can be your friend for your crew... but book early, cheaper hotels fill rapidly in advance of fairs.
**RATES REVISITED: It's possible that some fairs could be a little more malleable with their rates if they can be convinced that your attraction will bring in revenue that they wouldn't have gotten had you not been there. As opposed to performing dog shows, barber shop quartets and defunct family circus acts, I think it's entirely reasonable to think that you could convince a fair that haunted attractions are capable of drawing it's own crowd who might just come out to specifically to see your well marketed House of Horrors. With your pro experience, I'm sure that you could demonstrate that you have the ability to fire up your own well-oiled marketing machine. They'd like that. Just be prepared to work WITH their marketing department.
LASTLY: A great resource, really a must, is IAFE, the International Association of Fairs and Exhibitions. This is a well organized association that virtually every reputable fair, vendor and entertainment belongs to. They publish a book that among other things, details every event in the country (and beyond) including contact information, grounds size, demographics, attendance (attendance is a number you really wanna look at!) and other useful tidbits.
Hope this has been helpful. Holler at me anytime in a PM if there's anything I might be able to add. As I mentioned, we've been looking at this option for a while, but being involved in other things, haven't taken the plunge with a haunt. So we're looking forward to a 'guinnea pig.' Ha! Best of luck!!!