For the benefit of the OP:
“The apostolate should always be exercised in a saintly manner, with such purity of intention, such interior union with God, such generous forgetfullness and abnegation of self, and with so great a love for souls that it [the apostolate] flows from the interior spirit which informs it and at the same time nourishes and renews this same spirit.”(Pope Pius XII, Motu proprio: Primo Feliciter)
So, the interior spirit of the apostolate would provide its own maintenance by its members raising the bar in their ascetical or mystical life. A good question to ask the self - Why not make the opportunity available to the public by ‘schools’ of prayer?