Just use old balls.
They may not have much hair and be a little slow but it is the same for both players.
In fact a bit more entertaining than 250km/h first serve (that nobody can see) and better for the environment.
Even 10 year olds use a set of new balls per match in league plays. Not that it makes much sense, but that's how it is.
What happens to the balls after the match? Do they get ground up and shipped overseas for recycling?
The children take them home or the coach collects them for practice sessions.
Are we savages or what?
Actually I was not. But I think I see what you mean when reading it again.
Well, he is bar bar bar.
They do make "pressureless" balls that arguably last a bit longer (which no one in the US uses it seems), but pressurized balls will go flat even if they're not being used if they're opened. Wilson has a new plastic-free ball that uses similar tech to pressureless called the Triniti, which attempts to solve the plastic part and they last about 5 sets plus.