I have yet to see a drastic increase in sales from paid ads but some people swear by them. One thing to remember with ads is that most people need to see the same ad about four times before they act on it. So if you are going the ad route, remember that it is for the long haul. It may take months before you see any effects.
How can you do this the cheap way? Occasionally, I get coupons for free $100 worth of advertising on Google through my hosting company Just Host. You better believe I take advantage of this. If you want to sign up with Just Host so you can get these coupons as well, just click on the link on my left side bar.