Is it going to be a bike chaplain or is he going to be on foot?
Here are my two custom Chaplains:
"Chaplain Shoulder Pad" is a the wreath shoulder pad (either Sternguard or Vanguard) with a skull glued on (both were sanded to make a flat spot to glue it to. Some chain from the jewelry section at the craft store with the terminator honors attached, and the beat-stick from the metal jump-chaplain model. I just cut it at the wrist and attached it there with some counter weight in the base to keep it from falling over. The head is from Anvil Industries and you can get a bag full for a pretty dang good price, they even have hooded versions if you are making a chaplain for a rope wearing chapter (you didn't mention what chapter you are using).
The Jump Pack chaplain uses the Lord Executioner model as the base. I just cut off the top of the hammer and replaced it with the top of the Terminator Librarian Staff. You are using $40+ worth of models for a single chaplain now, but I had a letfover libby

. It's another Anvil Industry head and I just glued a raven skull on his shoulder pad.
Edit: looks like you are playing Dark Angels, so here are the roped heads at Anvil, they cost a whooping £3.00: