You can do a search for the flights you're buying on ITAsoftware. If you get the same price (bear in mind that the ITA prices don't include the Gastos de gestión), go into the booking details and find the fare class.
Alternatively, book with an online TA such as Expedia. Most of them charge you booking fees much lower than the ridiculous €12 the UX website wanted on my last (domestic!) booking.