You can probably get something going for less than $20-40 (more bandwidth and traffic = more ) a month, at first. Just find a hosting plan who supports PHPBB3 (an alternative of VBulletin). If you want to buy VBulletin it’s $180 for an owned license and can also be a month to month. I’ve never worked with VBulletin so I’m unsure whether or not it’s easier to run than a PHPBB forum. It may have different options and all.
As for setting it up this will take time. Be sure to plan everything out before starting. Know what you will name your forums and what there discriptions will be. You’ll need to set permissions, colors, set up extra features and options, etc… there are thousands of things you can do with a forum. I myself am an amateur, though. Also, people will not just come flocking to your forum, it takes time for material to build up so different discussions can be made. Unless of course you had 5,000 people just waiting to sign up…
Once you’re up and running you personally should have no problem running the forum alone for a little while. But once your clientele becomes larger things will happen and your members will want you to take different actions. This is when you’ll need more support such as administrators, moderators, and such. It works like a business in a sense.
Now that business is steady you will want to make consistent back-ups of everything. I can’t give you details here because this is where me being an amateur comes in. You need to do this just in case something happens and data is lost. Hackers, etc. Basic security functions should come with your hosting though.
Over-all I’d say just a handful of people can run a forum like this one as long as there is always someone on watch. If this was a full-time job for everyone you can figure paying out anywhere $20,000 a year to $40,000 a year, or whatever the heck you want to pay your employees. That’s up to you. For income you have your clickable keywords, promotions, banners, popups, subscription fees, fees for extra features, etc.
Now, if you want to get into purchasing your own servers, and doing it the real way… you’re looking as spending a lot more money. As this point you want to do everything professionally. You can figure spending $5,000 or more for your website to be designed and around that same amount or more for the equipment. Then you have your maintenance fee’s on top of that. While these things would be under warranty, you can’t just ship your server in to have it fixed… You’d have to fix it right away because you don’t want your site to be down for extended periods of time.
Go the easy way first, learn the ropes, then if you are successful purchase your own equipment. It may take a long time before it’s actually necessary. Forums aren’t the easiest thing in the world to make populated with consistent traffic.
FWIW in my experiences doing this.