[SYMM]

Registering a domain and getting hosting take no effort and cost peanuts.
For anyone who's not absolutely skint, and thinks they have a good idea, there's very little harm in taking these steps first.

The best way of getting people to visit a site is to have decent content. Aside from the listings, do you have pages containing helpful information for people looking to rent a house? (landlord tick-lists, 'things to consider', 'how much can i afford'...delete as applicable).
You need to make sure that the key information is contained as such within your page.
Have you used heading tags for headings? Are details like the location of properties given the prominence they deserve?

If your site is targetted at a particular geographic area, you obviously limit the market, but it will be much easier to personalise the site to people looking. Things like 'local schools/parks/shopping centres' will be of interest to people, and make you a little different to other places.
If you're not trying to target everywhere, and can find someone else doing a similar thing in a different area, you can agree to swap links.

setup some traffic-logging on your site and see how people are finding it, what search-terms they're using to get there and so on- this can help you focus your attempts to increase the current trends, rather than wasting time on areas noone is interested in.

paying for adverts is probably the best way to get people to your site though.