We've never advertised with them, but we do get a fair amount of business from organic searches on Yelp. If you haven't set up a free profile, do it. Then, I would suggest that you do general searches on Yelp to see where you rank on several searches that your customers may use: marble polishing, granite restoration, etc. You may find that your organic rankings are pretty good already. Those who advertise will see their ads pop up on the first page, even if the consumer searches for your company name, pushing you off the front page.
For my dollar, if I'm going to spend more on advertising, I'd go with Adwords or Bing.