I'd stick with SEO, blog commenting and link building are probably you best bets, article submisstion and what not. You'll be able to get some nice traffic for the first month if you invest $300 in the first month, I suggest you stick to $100/month for the first three months, you'll hopefully be able to get a OK pagerank in this time, then hopefully the money your earning from the blog, supplying you know how to earn good amounts with blogs, I doubt you will earn $300 in the first 3 months, but you should earn some money back, just keep on building up your blogs content and what not. With $300 though, I'd go with proxys if you want profit.