What is the distance from Paris France to Ljubljana Slovenia?

Distance by air is 966km or 600mi.
Distance by car is 1250km which would take about 11 and a half hours, cost 48.80 Euros in tolls, 116.28 in petrol and 7.60 in road tax according to http://www.viamichelin.com

Round trip airfare from Paris to Ljubljana is cheapest right now on Czech Airways stopping in Prague. The price is $298.50 USD round trip taxes in.

Looks to me your best bet would be to fly unless you want to have a car there instead of using public transportation.

For rail, unless you got a rail pass and planned on travelling more I believe it would cost you more than it would to fly, and it would take as long as it would to drive. Paris to Zurich is about 6 hours and Zurich to Ljubljana on a night train takes a little over 3 hours.