I just finished purchasing two ads, one in the verizon yellow pages and one in what is called the "yellow book" here in Fort Wayne. Most areas have more than one phone book anymore. The local service provider is required to provide a phone book the others are companies making money publishing books. Find out what the market share for each book is (dont ask the sales reps, research it by a third party)
Ask them about call tracking also, find out what each size ad will bring in number of calls generated, what the percentage calls that are closed is too. Be sure to get the figures for Tree Service, not overall. One rep tried to tell me all ads generate $14 per $1 spent on the ad. That is the overall average, but if you take out the biggies (lawyers, doctors, pizza joints, hotels etc) then the left overs (ie tree services) is much lower return.
The cost will also be based on the size of the population served. I am sure its far more to purchase space in Chicago yellow pages than it is the Smallville yellow pages. My city (Fort Wayne, Indiana) has population of about 250,000, and the metro area is around 400,000. I am paying about $55 per month for 1 1/2" display ad in the "yellow book" which has about a 30% market share, and $150 per month for same ad in the Verizon yellow pages.
Hope this was helpful, but be sure to do some research in your area to find out which book will generate more calls.
Terry