Step 1: Go to French train ticket (SNCF) website. Become extremely frustrated because they will not accept your American credit card.
Step 2: Call American credit card to see if they are blocking the transaction. No, more anger.
Step 3: Refuse to use Rail Europe because of ridiculous surcharge.
Step 4: Google. Oh miraculous, google, what would we go without you.
Step 5: Find capitainetrain.com (Update: They changed their name to Trainline)
Step 6: Google capitainetrain.com to see if it is a legitimate website and you aren’t about to be screwed
Step 7: Take risk and buy train tickets anyways
Step 8: Board train in France without the mark up. Happy dance.