You don't get paid per submit like freelancer writing, but if done correctly you can make very much extra cash this way. There are tons of websites with affiliate programs, and you can make up to 75 % commissions some places.
What it's really like to work for the world's biggest travel; Travel Writing Jobs - Become a Travel Writer; Discover how to get paid to travel the globe, stay in luxury hotels, experience exciting adventures, enjoy fabulous food, and view incredible sights; How to Become a Travel Writer: Writing Advice.