3D illustrations can be rendered to any resolution for use across various mediums. Higher resolution requires costly rendering hence higher price.
Instrumental sound is cheaper and voice-over comes at higher cost.
More the number of character/objects more the complexity and more the cost for animation.
More the number of seconds more your pay.
Usually, 3D is more expensive, 2D animation is more affordable, and 2.5D lies somewhere in between the two.