Mindless Spirits (10 gp): While it's possible to capture the vital essences of
vermin, basic
oozes, and other such unthinking creatures, these paltry spirits are worth very little.
Animal Spirits (25 gp): This category contains creatures of
animal-level intelligence, whose spirits—while presumably worth something to some deities, as reflected by the value of
animal sacrifice—are rarely traded in the soul markets. In fact, though the existence of
animal spirits is undeniably real, there's rampant debate in many societies over whether such things truly count as "souls."
Basic Soul (100 gp): This is the soul of a standard intelligent creature—a commoner, a low-level adventurer, a sentient monster of low CR, or any of the other hordes of weak or mundane folk who live out their lives with a normal amount of pomp and excitement. This is the lowest category of souls which interests
daemons, who see
animals and other nonsentient creatures as hardly worth the time to destroy.
Noteworthy Soul (500 gp): The souls of mid-level characters, rulers, famous or influential people, and other powerful, accomplished, and otherwise important people draw greater attention than basic souls, and drive bidding higher accordingly.
Grand Soul (1000–5000 gp): High-level characters, great heroes,
dragons, powerful
aberrations, and other such spirits of fabulous power and forceful personalities offer equally significant rewards to those who manage to contain their essences.
Unique Soul (priceless): For the truly unique souls—those of legendary figures, epic heroes, and other massive presences—there can be no going price. The unique sparks that live within these creatures are valuable beyond compare, and the frantic bidding (and backstabbing) that arises when one of these trapped spirits comes up for sale is the sort of thing fiends and
undead wait thousands of years for, paying nigh-unimaginable prices for the right to consume or display such an artifact.