St-Arnoult-En-Yvelines

So I really really want to go to the start of Paris-Tours (pro bike race) on the 12th. Problem is, I have no idea to get there. The start is not in Paris, it's actually in a town called St-Arnoult-En-Yvelines. The only way to get there is a commuter bus, that does not appear to run on Sundays. I'm debating just taking the train to the end of the line (10 kms away from the town) and hoping I can find my way the rest of the way (maybe a cab?). Any ideas?