March’s free and reduced-price companion volumes from Faithlife include:
Logos: Paula Gooder, This Risen Existence: The Spirit of Easter, and for $1.99, Dennis Ngien, Fruit for the Soul: Luther on the Lament Psalms
Verbum: Bonaventure, The Life of Saint Francis, and for $0.99, Bonaventure, Mystical Opuscula
I haven’t yet found a dedicated Spanish “free book of the month” page, but the past several months have also had on offer a free Spanish resource. This month’s is, in translation, A. W. Pink’s Reflexiones paulinas: Estudios en las oraciones del Apóstol (vol. 1).