Did I say social media already?
Social whatnow? No wonder I can't find new music - apparently you have to give up all expectation of privacy in order to find new bands.
Normal, old-school advertising is also available as a service. Instead of paying 95% of sales to a studio for a little ad spend, a band could pay 20% and hire the ad company themselves.
Oh definitely; and, to put a new twist on an old favorite, never underestimate the advertising bandwidth of the bass player's Astro minivan full of burned CDs and home-made t-shirts. Most of the advertising local bands around here get (besides their facebook and ReverbNation profiles) is word of mouth, spread by patrons, venue owners, and other bands alike.
Not to say that paying an agency for a bit of publicity isn't worth the effort.
Unless your band sucks.