it depend on the complexity of the certain headphone, work involved, as well as material, i can't give u a range.
if MS1 recable usually i charge RM 150.
ksc75 recable i charge RM60
some  other headphones like AKG K701  / Beyer Dynamic T5p / DT880 ect will be charge higher at range of RM 300-1K or even more depending material used.
still you can still get my work of Vero-150 cable for gold ring DR150, or Symphonica cable for Sennheiser HD650. that can directly plug into headphone without modifications.