Cost of train from Paris to Vernon?

The current fare is €11.90 each way (no discount for roundtrip).

I did this trip last Fall and have a couple of minor warnings/suggestions: see RS Paris book Tranportation section for good travel info, check the train schedule carefully as some trains take 1 1/2 hours to get to Vernon (many stops), go early in the day, hurry to the bus in Vernon because they leave soon after the train arrives (4e round trip last Fall), leave time to enjoy a crepe (or two!) on the terrace of the hotel behind Monet's home, and then make sure you know the return bus schedule to Vernon. I've been to Giverny twice now, once on a scheduled tour and once on the train. I much prefer the train since you can schedule your time rather than being on the tour's schedule (but they do provided a guided tour of the house/gardens). The exuberant French garden in front of the house (exploding with color) is my favorite but the better-known Japanese garden across the road is lovely too (and the inspiration for all the water lily paintings.

Thanks everyone for the great info.