That technology is not secret, they are “free” to build their own. Like every other company that builds broadcast platforms, if they want to play, they’ve got to pay.
But Parler won't need to do this - there are plenty of hosts who aren't going to join in with the coordinated effort to silence the speech of those who aren't on the 'correct' side. Info Wars and OAN are still on the internet.
Surely, if they wanted to, they could buy cloud compute resources from a company based outside the US. Why must they be on Amazon just for access to its web services platform?