You are planning to make up a few extra on those I hope... That is a great idea!
Hardly my original idea but the only ones I could find online were $45. I went to the military surplus store and bought the dummy grenade there for $12. I widened the hole in the bottom with a step bit, welded two nuts together then ground the flat edges of the nuts round, inserted into the grenade, and welded 'er up.
Nothing like driving across town to a mil surp store in the middle of a snowstorm and walking up to the counter and telling the cashier:
"I'd like one dummy grenade please".
"Pineapple or basball style?"
"Pineapple."
She grabs one from the rack of 100 or so behind the counter, hands it to me.
"Thanks"
"Is that all you came in for?"
"That's all. Why, is it abnormal to drive across town in a blizzard to buy one inert grenade?"
"Yes."
You know you are a weirdo when you are standing in a crazy gun store with the sounds of rented machine guns blasting away in the background and the pink haired pierced up employee is looking at you like you are the oddball.