Typical cost of AFCI breakers are $50 to $70 each, you should be able to check a Home Depot or Lowes. Take a photo (cell phone) of your existing breakers and take it with you to the store to get the correct make and model.
BE VERY CAREFUL IF YOU ARE DOING THIS YOUR SELF, my suggestion, turn off the main breaker first! also, do one breaker at a time, match wiring between old and new breakers.
Hope this helps.
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Pennsylvania, for 60+ years, most recently, Allentown, now TV. 
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