I would stay away from facebook, the conversion rate is most likely be low. There are a lot of threads on here about that, and how people lie about their age and how tough it will be to hit your target market.
If you are out of the US, you can get a license for google adwords, there are some threads on here about that too. That would be my first choice however you can always email other webasters and see if they would like to do a link exchange to advertise your site with or without paying for it.
Youtube videos are great ways to market your website, and other videos sites such as vimeo.
Print advertising is a good way to market your website, you can have brochures made up, business cards, ext.. For instance your niche is sports betting you can give them out when you are at happy hour or at a game.
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