When the Parish Priest is on holiday, I make a note of all the mass requests and donations. Sometimes people can't afford a donation, but the Mass will still be said.
The majority of the money is actually sent oversees to mission schools etc to help those who need it more.
It doesn't go straight into the priest's pocket, as some think.
Of course there will be priests, who are materialistic, just like in secular society. Please don't tar them all with the same brush. There are many who are humble people, who would give people in need, their last penny.