You could use airbnb as an example here.
Their search for houses to rent IMO is a bit rubbish. So build a better site with a more comprehensive search.
Everytime someone books through your site it redirects to their payment processor and you get a cut.
Sure would cost quite a lot to outsource all of the building of that but if you are good at making websites, both clientside and serverside you might be able to pull that off yourself.
What I love about affiliate marketing is that it is passive income.