Priests can generally get habitual permission for two or three Masses, especially on Sundays in large parishes when they are needed the most. However, at least in my home diocese, priests cannot benefit more than once from a Mass stipend in one day. Therefore our parish have special policies in place to make sure that priests do get paid from that first Mass of the day. That is something to keep in mind when requesting a Mass intention, especially if you are trying to negotiate for a reduced or waived donation: the priests depend on that income from offering Masses. It is non-negligible for many of them.