your parent comment got more than 120$ of benefit in a single order; if you amortize the cost of that prime membership across a year and use it like this it certainly seems closer to free.

I was in similar situation not long time ago, and they wanted to charge me some money (around $100) for TV setup, even I am prime member.

That parent comment is now also locked-in and will justify Amazon's extortion to themselves by buying more things from them without bothering to check other stores.

They end up paying quite a bit beyond that $100/year fee.