phorum or phpbb would be good solutions, and both are easy to install if you know a thing or two about web databases. I've done it a bunch of times.
they're both free, and you'll need a website to host them on. There are tons of options for hosts, and you should be able to find one that'll work for you for around $10/month(maybe a few dollars less or more).
get it setup and running, and you shouldn't need much direct involvement if you set everything up right. You may need to spend an hour or two every couple of months to install updates to the bulletin board software and do any general maintenance, but nothing much beyond that.
email me if you have any further questions.
good luck.