I assume you've done direct email to past customers? Personally, I have serious doubts about most paid advertising these days, when it comes to the little guys. It just seems like it takes outrageous amounts of money to make anything happen, and I think the public has become so accustom to ignoring ads, it's really like beating a dead horse. I'm sure it works for some people, but I don't know how. Could you maybe pay somebody who really knows what they're doing, to boost your SEO?
I still think a good heavy youtube campaign of instructional/promo vids could do wonders. There's a guitar store I've bought stuff from that does all kinds of vids. Works well for them. I would also look into creating your own product line... Nothing gets you out of the rat race better than having stuff nobody else has.