phpBB Spam

We have a phpBB forum with some spam issues. Almost all the internal settings are on. Your job is to install 3rd party addons to combat the spam. We want to know your plan of attack before you install (like what you are installing). I've also had to turn on CAPTCHA for user reg - I'd like to turn this off or replace it with one that is easier to use but protects against spammers. Please address this in your bid. PMB for more and link. Budget is $50 or less.