The last time I searched for EP's they all sold them at the same price as RE. I think they are the distributor in the US to others(?) The prices may vary if you buy from a site outside the US since the exchange rate conversion kicks in.
If you go to
www.sncf.fr and select English and then "buy a ticket" you wind up on RE's site. A few other countries have been "roped in" by RE.
PS: Shipping costs and extra perks can change the end cost of EP.
Raileurope is the U.S. ticket office for SNCF, SBB and I think one or two other railroads; of course they will direct you to Raileurope if you use their site. Other companies also sell Eurail passes. One is in Florida, one is called Eurailpass or something like that. Some include mailing in their prices, some don't. Some offer sales on tickets for old people, some offer special winter sales. Some offer discounts and suddenly inform you they no longer apply. It pays to compare prices and terms. Some country passes are not offered under Eurail, e.g., Germany. In short, spend some time on the internet.