Please don't listen to Screamline. If you invest $350,000 the first year you open your haunt you will go bankrupt and you will hate the haunt industry you've come to love. Now lets be realistic here. It's not going to be cheap starting your own haunt. But all the top haunts started off small for the most part and you can too. The costs that are going to be involved in starting your own haunt are
-Advertising (this includes your website, flyers,etc.)
-Actors (unless volunteer)
-Signs (sign before you enter parking lot and sign on building)
-Food for concessions, media events and workers
-Sprinkler System (unless it's all outdoors)
-Building Materials (Wood, steel, nails etc.)
and so on and so on. You may be able to get free materials if you have Home Depot Sponsor you. That could be the cost of sponsorship.
When it's all said and done it should cost you around $30,000-50,000 to start off small and over the years you can improve with the money you make off your haunt. But to make a profit depends on how you market your haunt, your location, the quaility of your haunt and so on and so on. Make sure you have great parking and aren't in the middle of nowhere. The closer you are to a major highway, the better.The only reason you would need to invest $350,000 is if you're planning on buying lots of animatronics and are really trying to promote your haunt the first year. But what I would suggest is be creative, advertise anywhere you can such as online, festivals, parades, cross promote with other haunts etc. You don't need a TV commercial, a billboard or even a radio ad. But you could get one created to add to your website for under $100.
You need to have enough knowledge of how things work in the industry before you begin your venture in the haunt industry. You can't think that it's going to be as easy as your home haunt because it's not. It's going to take a lot of dedication and you'll be making a lot of mistakes that can either make you or break you. But be smart with how you spend your money. Your first year you should use volunteer actors, use mostly masks and cheap makeup to save on time and money and just be creative. Make sure your haunt has an interesting back story and theme your haunt so it matches the back story.
There are many haunts out there that are actor driven and rely very little on props and fancy sets. Buy old furntiure for scenes from flea markets, yard sales or good will. Get your friends and family involved so you can save on the costs of workers. But make sure they are reliable. Find a good company to design a really nice proffessional website with a nice banner included and advertise and exchange banners with sites.
There are many haunts out there that don't have huge budgets, but have a big following. Just be creative and smart on how you budget your finances and please make sure to advertise cost effectively and learn whatever you can about starting a haunt from anywhere possible. There are a lot more things that I could suggest you do, but my fingers are getting sore from typing. I know haunts that have started off on a $10,000 budget and have made nearly $100,000 their first year. It just matters how wise you are about what you do and focus on the right things.