A sword portion is pretty standard for me with a GP birthday party. They love it and it makes their party more fun. Same for cane with an arab audience. If someone requests a prop that requirs more TIME, like doing it in one set then doing your reg. set then it is extra and I do explain that is extra due to extra time spent at the gig.
I offer two props for clients for a show they can choose. Most often it turns out to be veil and sword though. Nothing wrong with them loving sword.
I would not think of charging more because I do them though. I do what I feel I am good at and make that offering. If you went out to eat you would not expect to pay less because the place did not have certain things on the menu. You just pick a place that has what you want in the first place right? (not saying that we are like food)