There as plenty of free or cheap forum software out there, Assuming you have hosting with your domain with all the relevant access and extensions.
Its a question of figuring out what software you want to use. i used phpbb and found it to be pretty good.
I am hosting my own domain on my own server, and I'm pretty sure I've enabled everything.
Thanks for your help.
The two mainstream forum programs are phpbb and vbulletin. phpbb is opensource and free. Vbulletin costs about $75 a year or so and many folks (including myself) believe it's well worth the cost. I recommend you use vbulletin (and I've used both on busy forums).
The second point is that even if things go well you are still looking at probably about 2 years of you promoting and posting to a mostly dead forum before it gathers any life of it's own. Maybe other industries have better numbers, but in both the forums I've started, they both had that two year timeperiod of hard slugging. It gets wearing after a year - continuing to find stuff to post when it seems like no one is reading.
Vanilla forum is another great open source platform to try :)
I'm a fan of SMF, another free and open source forum. Its pages load faster than vBulletin, IPB, and some others.
wheel, thanks for the advice about "2 years", which although cautionary is also reassuring.
I agree with the advice to keep posting interesting things (not junk) even if it's just you talking to yourself for a long time. Every once in a while someone will drop by and see that you have interesting things to say, and you'll get the occasional visitor who comes from a search engine looking for the answer to a question you've posted about.
Most forums do not reach critical mass.
First make sure that there is not an established forum in your niche that is so firmly established that nobody would dream of going elsewhere.
Do you have connections with existing enthusiast groups? Use them to kick start interest (after priming the forum with a few topics). Don't forget press releases to printed enthusiast magazines and newsletters.
The technology is the easy bit.
I agree with piatkow - make sure you get a website with a bit of recognition and traffic first, otherwise you risk to spend a lot of time on setting up a forum that nobody uses.
If you have access to cgi might look at e-blah. Has the ability to be simple (flat file) for grow to mySql as the need arises.
In any event, setting up a forum is 1/10th the effort. The remaining is getting in gear, posting, gathering new members, and growing from there. Takes time and effort.
Test drive some of the forum software here: