If the dev was fair, he would split the revenues of all the models with the instances to keep them alive. The free API call doesn't matter if the instances close.
You will attract the fanboys base. But, I second this. People should give the same amount of money to an instance before giving to these closed apps. Without the instances, they couldn't use the apps.
I saw a lot of comments about hashtags to follow. It's right. You must follow them to find people to follow.
But, it's missing a part of how to find people to follow. Boosting is essential. A way to boost automatically a toot is to use groups. You mention the group about the topic and your toot will be boosted. You need to follow these groups to find people. You feed will be less empty by following groups.
And at the beginning, it was like 1$. When you have the full history, it looks like another raise of the price.