Local websites indeed have some additional site promoting challenges. For my local taxi website, I am also looking into inexpensive ways to promote the site.
My collegue at my daytime job -who has been a taxi driver before for a while- suggested to have a small deal with some local restaurants so that they can have a free advertisement on my website while the restaurants can call my number or give a business card when one of their clients wishes to order a taxi. Same deal can be done with other local businesess where foreigners go like conference centers, event halls etcetera.
In your case, instead of a phone number, business cards with your URL can be provided. Or, what about to have a dedicated taxi page and have some taxi companies have your cards or urls displayed in their car in exchange for a free ad on your site?