Depends on how popular it is. A lot of the larger niche boards are paid for. Expect about ~$10 a month if your board is too large for free hosting.

Your best bet for finding a decent host is to peruse http://webhostingtalk.com/ for a few hours, finding links to well-liked hosts, and then comparing plans across them. You generally get what you pay for.

I can vouch for Site5 and Dreamhost. Site5 has amazingly fast response, and Dreamhost has a lot of bandwidth available for cheap.