I have spent the last 5 years building an email list to generate traffic with little thought about SEO. I think I've gone as far as I can with opt in subscribers and am now looking toward SEO. I have a budget of $500 to $1,000 a month to spend on marketing. What should I be concentrating on? Link building? Hiring writers to generate more content? Will an SEO firm look at me with this small a budget?