Trap the Soul

Note that items with the Trap the Soul (item enhancement) have no Hit Die requirement or material component.

Material Component cost
Thus overall costs for your standard component supply (Stack of 1000) are:
 * One Tiny Khyber can be purchased at the portable hole. It's base price 100pp, and be can lowered via haggle.
 * Tiny: 100,000 platinum
 * Small: 500,000 platinum
 * Average: 1,250,000 platinum

Khyber Fragment Conversion cost

 * One small can be created with 500 fragments
 * One average can be created 1250 fragments

You can usually find 1 fragment for 1pp on AH, though at that price you are better off buying them at the portable hole.

Soul Gem distribution notice
When in a group the soul gems you create by using this spell can be picked up by any member of the party. This should be considered before using this relatively expensive spell.

External References

 * Trap the Soul, 20-30 HD results thread, by Angelus_dead
 * List of Soul Gems (colors, description text)