I mentioned, under Gospel of John resources, the excellent short commentary by Richard Burridge in the Daily Bible Commentary Series – probably focused on laypeople, but I found much rewarding material.
Someone pointed out to me that CBD currently has all books in this series for only $2.99. (Amazon: $12.95)
I also noticed that this generally unrecognized series does boast some eminent scholars:
Loveday Alexander (Acts)
Francis Moloney (General Epistles)
Dick France (Pastoral Epistles & Hebrews; also Mark)
Jerome Murphy-O’Connor (1 Corinthians)
James Dunn (Romans)