Allow the items to be unlocked by completing the achievement & purchasing one of the item from the vendor. At this point you can purchase additional for gil from a new housing item event npc (available year-round), but all event item now have an ownership tag. Any furnishing with an ownership tag will be removed from an estate if it's owner is removed as a tenant/fc member. The item will be deleted with warning if anyone besides the item owner attempts to place the item in their bags. They could add unlocks to the mogstation purchases too, which would make $5 food actually worth the price since it could be replaced via a gil purchase instead of actual cash if someone ate it. The mogstation part would require them to go through code redemptions if they were to apply this to previous items, so probably more work than they'd be willing to do.