When buying an iPhone 5S will I need to pay extra for a sim card?

I currently have an iPhone 4S. I'm about to upgrade to the iPhone 5S and I understand that it has a different sim card. In total the iPhone comes out to $812.00. Will I need to pay an extra $20 on top of that to pay for a new sim card? Or will apple provide me with the sim card?

Depends on which carrier you plan to go with. I know at T-Mobile you can basically get a SIM card for an UNLOCKED iPhone 5S. Other than that, all the other major US carriers lock their iPhones to their service. So if you buy an iPhone 5S that was from Verizon/AT&T/Sprint for example, no… You can't just pop in a SIM card if you're with a different carrier. You should really do some research next time before you make a huge purchase like this and spend almost $1,000 when you most likely won't be able to change the SIM.

PS Apple doesn't sell SIM cards. None of the carriers do except for T-Mobile.

Not sure exactly how you're doing it but:

If you buy the phone from Apple unlocked, then you can use it with any carrier e.g T-Mobile. If you contact your carrier, they should be able to provide you with a free Nano Sim which is the one needed for the 5S. They can then transfer your other SIM card to the new nano sim, so you will not need to pay extra.

Most Providers do this, you should probably contact them to find out. Hope this helps.