MiaCharlie, I agree with
ldsant. The prices in Paris will most likely be cheaper than in the U.S. due to the favorable exchange rates for the dollar right now.
The Thalys train has its own web site:
www.thalys.com
There you will find schedules, prices and other info in English. You can purcahse your tickets in PAris at any train station, SNCF boutique (national rail service), or affiliated travel agency.
The Gare du Nord is in the 10th arrondissement while the Tour Eiffel is in the 7th (bordering the 15th). It's an easy Métro ride or you can take a cab.
There was another thread recently on the Thalys:
http://www.flyertalk.com/travel/fttr...ML/006278.html