My thought is that you spend a little on getting close to the top on the organic listings in google.....and spend the $600 on yelp. Assuming Yelp is a big deal in your market. Here, it's not worth the time.
My math shows the usually Google outperforms Yelp dollar for dollar. Yelp is very expensive and they post your listing in a lot of non-related categories. I've spent hours discussing this with them and have asked for some data and references. They use a soft sell and will not share data or give references. That says to me that the cost outweighs the benefit. Be careful with them.
Dollar for dollar Adwords for sure, hands down. If you want to spend money on yelp do the deals. That way you only spend when you get a customer. I get a 4 to one return on adwords.