Does anybody know of a safe, cheap egg stamper for keeping dates? I browsed Amazon and found a good one- but it's 20 bucks and I'd prefer something cheaper. Any info and reviews are helpful! (If I have to, can I use a classic China-marker? I've used them for hatching eggs but not for refrigerator eggs.)

My hens jump back an forth in production. This summer, I've been getting a good amount. But when it gets too hot... they don't wanna know nothing! 
