I come from a city of 150,000 and this is my model on those sites, lets say it's for dentists as per your example
I build a html home page with a big box for "featured dentist" down the right third of the page. This gives a bit of a blurb about the dentist and his practice, the featured dentist also has a page called featured dentist.
Then my content fills the rest of the page and then down the bottom a list of all the dentist in the city - these are not links nor do they include any contact details, just the dentist office name.
Then I build 4 separate pages for dentist listings - my city can easily be split into 4 - maybe more or less for other areas.
I charge on a sliding scale charged quarterly
featured $250 quarterly
listed 1 $150
listed 2 $140
listed 3 $130
listed 4 $120
obviously the higher you are listed the more they pay.
the example here probabluy gives you a better ideawhat I'm trying to describe
