Logos has several Yale Anchor Bible commentaries on sale this month. Fitzmyer’s Romans volume is free and most importantly for us, J. Louis Martyn’s Galatians volume is available for US $2.99. Click on the direct link or head on over to their free book of the month page and get them all.
For those of you unfamiliar with Martyn he taught at Union Theological Seminary in New York City from 1967 until his retirement in 1987. His Galatians commentary was published in 1997. For more information you can read Beverly Gaventa’s tribute written after his death in 2015.