Since you continue to post about it...yes
You're right, the cost of shirts is irrelevant. Free shirts for everyone because the cause is good. Even if they can't actually pay for them.
Maybe they're thinking this would help raise awareness and instead of being able to afford $15 in flyers, they could afford $150 or $500 since $15 wont get you far. Maybe they could add additional resources or increase the reward money. Maybe there has been a loss of income during this. None of the above do I know so I'll reserve judgment.
It's not uncommon to charge for shirts to raise money for various reasons. It seems in this case people want a detailed report of how that extra couple bucks made is being utilized.
Is it a ploy? I don't know. I'm more concerned with the circumstances surrounding her disappearance than I am about them becoming hundredaires from slanging t-shirts.
It seems as though you already have your mind made up so if I were you, I'd probably pass on purchasing a shirt. If you want to support them you can volunteer or print some flyers and ship them to the volunteers if you're not a local