Accoding to the English language page of the Bahn website for the Rheinland-Pfalz-Ticket, the price is €27, €19 for the RL-P-Single ticket. According to the German language page, it is €28 and €20.
Do they really charge less for English speaking travelers? According to www.der-takt.de, the official website for regional transport (Nahverkehr) in Rheinland-Pfalz, the prices are €28 and €20. I think the Bahn just failed to update the prices on the English page when they went up in December.