I had a devilish idea. I hope nobody actually does it, but it's fun to think about it. You know how a lot of ebook sellers will do the "it's $19" thing, then in a few weeks say "price goes up permanently to $200 next Tuesday" to try to pressure people into buying?
Put it on your own site. Don't tell anybody. Sell it for a really cheap price, like $10 or even $1 if you're really brave and have servers that could handle 1000 downloads in a day, and write on the page that every day the price goes up by a dollar. Update every day. If your page gets any casual traffic for other reasons, someone will sooner or later notice and tell a friend (or, if they don't have any friends, tell an enemy). People will be motivated to buy today, those who hear about it a few days later will have missed out on the lowest price but hey, it's still pretty good, and by the time sales grind to a halt you might have made a couple thousand bucks. Do that with another product a few months later, and people WILL be checking updates to your site.
REAL gimmicky, but in an era where even developers who rarely did sales are doing bigger and bigger ones, going "nah we're never dropping our prices, in fact we're gonna keep raising them and there's never gonna be a better day to buy this than today" is, if nothing else, a way to get some "did you hear about the crazy guy who's raising his prices every day" word of mouth.
I've never bothered with advertising, though someday I probably will, when I have a product that I think will sell well enough without advertising. What I mean by that, spending $500 to double the sales of something that would otherwise make $400 during the period the ads run, not doing that. Spending $500 to double the sales of something that would otherwise make $1000 - now that's worth trying.
Without advertising, I just post about stuff here, KVR database and forum, a single Facebook group, label Twitter and audio production deals Reddit. I could skip the last two and lose maybe 1-2 sales. Though I do have a site that's got a good amount of traffic from people looking for free stuff, so that is also good for getting the name out there etc.