In my opinion, if your board is good enough, they will come.
I've never spent a penny on advertising.
The last board I set up has been going for 12 months and now has over 2000 members and I haven't paid to advertise it anywhere.
Good topic here on how to attract new members
http://www.phpbb.com/community/viewtopi ... 6&t=362219
People will join if they're searching for what you're talking about and your board looks interesting enough to join. That involves content. Get the content from several members and it will look enticing. Putting a link in your sig on other boards you post on is free too as long as it doesn't contravene that sites advertising rules.
Presentation has a lot to do with it. We see a lot of new boards with dozens of empty forums or lots of forums where all the posts are by the same person. They either look deserted or like the home of someone talking to themselves. You have to make it look interesting and there are a few simple ways to do that. Keep the number of forums low (less than 10) unless you REALLY need to expand them. For instance, many set up forums for tv, film, music, books, gaming with nothing in them when in fact one forum for entertainment would do the job until such time as you have enough topics on one of those subjects to warrant a new forum for it. If it's brand new, make some fake accounts and post to get the counts up and make it look like people are chatting. It's amazing how much that will bring people in. That can be useful even on a fledgling board. Make up a 'character' who disagrees with every opinion. People will soon step in to post that they're wrong and that gets the chat going. Get a team of 2 or 3 members together to think up ideas for things to post/chat about. Get a little competition going. If people post photos a lot of the time do a photo compo with voting. Doesn't need any prizes but it gets people interested.
So, personally I think money on ads is a waste. Make your site worth visiting with content and your google rank will go up on its own. Reading one of your other posts, if your board is about fitness, sports and health, run off some A5 fliers and see if the local gym will let you leave a stack on reception. Costs you nothing. I think spending £400 on a local paper ad will be a waste of £400.