I'm an international PhD student, and before I started my PhD, I was required by my boss to pay a big amount of fee to the group, in order to cover my research project.
He said I can't use the group's research grant for my research project, because I'm not a tax payer in this country. The group's money is funded by taxpayers. And he said the fee I was going to pay is for my own experiments and travel expenditure for conferences. He said I came here for my own PhD, so the group doesn't owe me anything and isn't going to pay for my own research.
I was younger and naïve at that time, so I thought that was fair. I paid.
Later the money I paid was used to cover my experimental materials and my trips to conferences. But only a small portion of the money has been used. My experiments didn't go well, so I didn't buy so much materials over these years as we predicted. Also, I've only been to three conferences. I'm already in my final year, but much of the money is still unused.