If you are looking to build a directory website then you need to plan very carefully how it is all going to work. You need to think about how you are going to allow people to sign up or if you want to manually take the sign ups and add them to the website yourself. This is often the cheapest way of doing it but does mean there is more work involved for yourself, adding your businesses to the directory.
The programming of a directory website is very important and for that reason you need to ensure you use a competent web programmer. You may have to fork out a bit initially to get it all p and running, but once this has been done, you can then start to make money back either from taking money for people to register on the site or by selling advertising space on the site. To sell advertising space you will need to show your potential businesses the amount of traffic your site receives and give them some sort of statistics as to how many clicks on their advert they are getting etc.
Directory websites are not for the faint hearted but can generate a good income once up and running.