Managing Monthly SEO budget

I keep on going back and forth on how I should divide our budget. I was wondering for the small businesses out there, how much do you set a side for monthly SEO budget? Do you divide that budget between SEO and PPC?

That would depend on what's converting. Budgets usually are for people who don't track their Return on investment, because if you did and knew for every $1.00 you spent you got back $1.50 why would you limit it? You wouldn't unless you are dealing with something you can't manage at the current time, and in budget you then refer to people to hire to do it for you, which does make it confusing at first but still you would only limit to your net income decline from paying people or services.