For my single user instance, I can be charitable and say that it’s running on hardware that I already had that is running regardless on spare otherwise unused resources with a already registered domain so the only cost is time spent setting it up. Or I could apply all the costs from the server Lemmy, then it would be about $1200 initially plus ~$10/mo per user.
As a policy I don’t answer the phone with an unknown number from any area code except my work HQ, I don’t answer the door for anyone that looks like they are paid to be there, I don’t open mail if there’s any hint it might be a mass mailer. At the end of the day, no matter what methodology they use, they are always going to get a bias from people who are willing to participate and be contactable.