Stone familiar cost

[TheTheos]

Does it cost gp to store a spell in stone familiar? Is the cost same as for wizard to write it in spellbook? Or is it for free?

Stone familiar wrote:

Aura faint abjuration; CL 3rd; Weight 2 lbs.
Slot none; Price 6,000 gp
DESCRIPTION

This life-sized carving of a Tiny animal is crafted from dark, rough stone. It has a hardness of 8 and 20 hit points. A witch can use the stone familiar to store up to 500 levels of spells (cantrips count as 1/2 level for this purpose). A witch can use the stone familiar to teach her living familiar any spells stored in it, and vice versa. A witch who identifies a stone familiar immediately knows what spells are stored inside it. A stone familiar is never found as randomly generated treasure with spells already stored in it.
CONSTRUCTION REQUIREMENTS

Craft Wondrous Item, share memory, creator must be a witch; Cost 3,000 gp

[Markov Spiked Chain]

I would assume they use the same rules as a witch teaching spells to their normal familiar. Level up, learn from another familiar, or burn a scroll.