how much does an Apple sim card kit cost

I cannot seem to find information about it in the online store, but this is from a support document about the Apple SIM.

Apple SIM card

Wi-Fi + Cellular models of iPad Pro (12.9-inch), iPad Air 2, and iPad mini 3 and later might come with either an Apple SIM card or a carrier SIM card in the SIM card tray.

If your iPad didn't come with an Apple SIM card, you can buy an Apple SIM kit at an Apple Retail Store in the United States, the United Kingdom, Australia, Canada, France, Germany, Italy, Japan, Netherlands, Spain, Sweden, Switzerland, or Turkey.

I suggest you call the store you intend to buy it at and ask. Please report back if you do, as the information may help other users in the future.