http://www.d20srd.org/srd/magicItems/rings.htm#spellStoringMinorbut even more minor, limited to one spell level instead of three, and unslotted.
Spellgem price is 66% of a level 1 wand, and a minor ss ring costs 50% more than a level 3 wand, so the price is probably too low at 500. Pearls of power for level 1 spells are also more expensive at 1000.
Using wands to figure the difference between a third level spell and first level spell gives a factor of 15. Apply that to ring of minor SS gives a price of 1200 for a 1st level ring, 2400 since it's unslotted. 1200 is for a spellgem that takes up a gear slot, like a ring. That's more gentle than basing the price on extrapolation from the rings of spell storing, 10,000 is a bit too much for a level 1 spell storing item.
If based on ring of SS, the caster level will always be 1, the minimum to cast a level 1 spell.
Are Spellgems supposed to only cast spells on the user, like potions? Or can you store a magic missile or charm spell in one?