It's free only bro.. for me the sim was door delivered by airtel representative within 2 hrs of request. (It's more than a year now)
may be the franchise or specific shops in your area may have been charging..
B/w why did u went to airtel show room..
You should have filled the details here -
http://www.airtel.in/4g/sim-swap
SIM would be home delivered in a day.