Pkarr is not free, in the same way sending few hundred udp packets is not free. It definitely costs something!

But joking aside, running Mainline nodes costs something too, mostly your time to open a udp port or setup a VPS, we are just amazingly fortunate that Bittorrent provided enough incentive to do it other than our idealistic goal of sovereign identities. 

All hail media piracy. 

 I qualified that in my next post.  I think it could be about 1 microsat. ie 1/1,000,000 of a satohi