I would only provide one link on a given keyword per page. SEs will only evaluate the first link to a given URL on a page, and a selected keyword should always be linking to the same URL throughout your site.
So the specific answer I would offer is once per page that the keyword appears on. For example most sites have a "Home" link in their navigation bar. That link will appear on every page of their site and it works fine.
You can alter the keyword or phrase and provide links to other pages. You can send "cars" to one URL, sports cars to another and luxury cars to a third URL and so forth without any concern. You don't want your page to look like a collection of links. As long as you do it in a quality manner you should be fine.