Forum Starting Budget
A lot of new forum owners make the mistake of assuming starting a forum is completely free. This is not true and any experienced forum owner will likely agree with me. Opening a forum is like opening a business, it will cost you more to run it and keep it open as time goes on and especially when you get more business or members and activity. There are numerous things that will require money to be spent including annual costs of the forum's domain name, web hosting, web servers once the forum gets super active, paid forum software if you decide to go that route, advertising, contest prizes and other expenses. Many people feel that a free forum hosting service will enable them to run a forum for free but they fail to read the fine lines of that services agreement. Once your free forum starts to put a dent on the free services servers, they will either ask you to start paying or result in a lot of downtime. And one disadvantage of having to pay a forum hosting service is that you cannot convert to self-hosted software so you are stuck with that hosting service in most cases.
There are two routes to go with, the cheap route and the not so cheap route. Both routes are good routes to take.
Go with free software! You will likely save over $100 for initial creation and over $10 a year for update costs of paid forum software. If free forum software works for you and does what you need it to do, then there is no valid or logical reason to have to go to paid software in order to be successful! Those who insist on being paid no matter what are a clique and should be avoided at all costs. Use what works for you and save your money for other important things such as advertising your forum and what not.
Not So Cheap Route
Use paid software if its features are what you need. In many cases, paid software provider will install the forum software for you, update it and give you private support. Those are the main features you will find in paid software that you will not find with free software. If that is what you need, by all means, purchase paid software. Use what works for you and your community. However, most paid software is over $100 for purchase and requires you to pay every so often to keep your paid license active. A lot of paid software is also more bulkier and requires more resources from the hosting so you may have to spend more money on hosting as well.
Active means more $
Once your forum starts to get more active, it will require you to spend more money. I started AAF on shared hosting paying only $110 a year. Now I pay over $100 a month for dedicated server hosting because it requires more memory and resources than a shared server can allow me to have. When AAF becomes a big board, it will likely need an upgrade server or multiple dedicated servers to run properly which will likely cost me a lot per month. I accept this challenge and am always preparing for it to happen. I create plans for budgeting for the future of my forums. If you just wait for it to happen without a plan, it will likely be overwhelming when it does happen. So you should expect the costs of running a forum to increase over time and it could be a lot quicker than you imagined. AAF is only about 2 years old!