Ring of Spell Storing store 5th level magic in any composition, rare, DMG cost 501-5000 gp, XGtE cost 2,000 gp.
My gem store up to a 5th level spell. They are crafteable, so they should cost around 250gp to 2500gp (DMG), or 1,000 gp (XGeT)... that sound very cheap, isn't it?