Freelance pricing

i am working freelance for a fashion jewelry designer after the day
job and on the weekends. i carve different types of wood, and
acrylic from models that i am given, also am asked to embellish
these models, by making them larger, smaller, more sensuous,
different proportion, more curvy, etc., also i am doing limited
production runs of 20 pieces or so, including pendants, earrings,
bracelets, a for instance would be that i am given an old piece
of ivory jewelry and required to make it in white wood, brown wood
and acrylic…, then they add the gold, stones or whatever, ok
my question is in my pricing; how much should i charge for model
embellishment work, 50hr?., 100hr.?Does it depend on the
percentage of change? Some of my changes are so minimal, but so
dramatic and make the boring original piece, so beautiful, that they
have been added and the original deleted, and the designer is
saying to me to please do anything i want in the way of change, and
accepts every one off that i whip up, with fervor, and begs for
more. I have been working for this person who is very popular with
neiman marcus, bergdorfs, etc, for only 8 months or so. This also
is not a letter of conceit, rather a question of my pricing. As
with alot of fashion jewelry the markup is often close to 1000%
above materials and labor(mine and jeweler’s), but that should not
have anything to do with my pricing right?, any ideas???, i’m
good with off or on list (@soulofwood), dp