Another one of the "you probably knew it all along" series, but to add to my previous comment about gods being able to upgrade materials: they ignore intelligence requirements, too.
Makes me wonder why even bother using SoCMs...
My guide to free phoenix feather limbs:
1. kill your elder using the banana peel technique and steal his book
2. lose your limbs with banana peels, beartraps, or broken glass
3. pray to Silva
4. repeat until she upgrades them to phoenix feather
The only cost is time, really.