What is the cheapest way to travel from Paris to Prague?

You should try the bus with Eurolines, usually the cheapest way to travel around Europe for a fair price. http://www.eurolines.fr/fr/promo ...

Avoid train which is crazy expensive in Europe. Check planes like other posts suggest (skyscanner.com , Easy Jet, etc.) . You can also try to share a car via French websites like covoiturage.fr or karzoo.eu