Buying individual commentary volumes, as opposed to commentary sets, can be quite expensive. However if you desire to have the best commentaries then there really is no way around buying individual volumes. I found some commentaries on Amazon that will be a little more buyer friendly, as they are used (there is one new volume however it's price is very low for such).
Buying used commentaries doesn't always work, it isn't always the best option. Some volumes haven't been out long enough for their price to drop. Others are now in the second or third editions. When they are in later editions/revisions, you can almost always find an earlier one for very cheap. Most of the time the later editions do not offer much more than the earlier ones, usually it has to do with a new cover design, updated bibliography, and maybe typeset. In those cases you can find the the older editions for very low. I have not been able to find anything significant which changed nor which should cause you to get the newest editions/revisions below. For Moises Silva's Philippians commentary, make sure you do get the second edition though, that is the one linked to:
Mark – William Lane (NICNT)
Romans - John Murray (NICNT)
1 Corinthians – Gordon Fee (NICNT)
2 Corinthians – Philip Hughes (NICNT)
Ephesians/Colossians/Philemon - F.F. Bruce (NICNT)
Philippians – Gerald Hawthorne (WBC)
Philippians – Moises Silva (BECNT)
Colossians & Philemon - Murray J Harris
1&2 Thessalonians - Leon Morris (NICNT)
Hebrews – F.F. Bruce (NICNT)
James – Peter Davids (NIGTC)
1 Peter – Peter Davids (NICNT)
1-3 John – Stephen Smalley (WBC)
Revelation – Robert Mounce (NICNT)
Buying used commentaries doesn't always work, it isn't always the best option. Some volumes haven't been out long enough for their price to drop. Others are now in the second or third editions. When they are in later editions/revisions, you can almost always find an earlier one for very cheap. Most of the time the later editions do not offer much more than the earlier ones, usually it has to do with a new cover design, updated bibliography, and maybe typeset. In those cases you can find the the older editions for very low. I have not been able to find anything significant which changed nor which should cause you to get the newest editions/revisions below. For Moises Silva's Philippians commentary, make sure you do get the second edition though, that is the one linked to:
Mark – William Lane (NICNT)
Romans - John Murray (NICNT)
1 Corinthians – Gordon Fee (NICNT)
2 Corinthians – Philip Hughes (NICNT)
Ephesians/Colossians/Philemon - F.F. Bruce (NICNT)
Philippians – Gerald Hawthorne (WBC)
Philippians – Moises Silva (BECNT)
Colossians & Philemon - Murray J Harris
1&2 Thessalonians - Leon Morris (NICNT)
Hebrews – F.F. Bruce (NICNT)
James – Peter Davids (NIGTC)
1 Peter – Peter Davids (NICNT)
1-3 John – Stephen Smalley (WBC)
Revelation – Robert Mounce (NICNT)