巴黎去布拉格要幾耐?

There are trains, but it takes I think at least 15 hours. You better fly.
http://www.raileurope.com/

Try some budget airlines, e.g. easyjet

btw, prague is still my favourite city, go before it is totally overun by
tourists (although it probably is already...)

Paris-Prauge

train 14-18 hours changes 1-6 times

Plane under 2 hours WWW.skyeurope.com