SNCF have a special winter offer running from 23 December 2017- 18 March 2018. The cost of a return ticket is only €12
“The Yellow Train is a unique and eco-mobile way to enjoy the charms of Cerdanya with family or friends.
The Occitanie Region and the SNCF offer you a single price: € 12 regardless of origin and destination between Perpignan and Latour-de-Carol, Enveitg, with a package valid from 1 to 8 days to choose.
By purchasing your “Yellow Train in Winter” ticket, you will benefit from a 50% discount on additional routes to reach Perpignan from all the stations in the departments: Aude (11), Gard (30), Hérault (34), Lozère (48), Pyrénées-Orientales (66).” ( translated from their brochure)
Link to purchase tickets and more information https://www.ter.sncf.com/occitanie/loisirs/activites-plein-air/offre-train-jaune#ancre