One's billing rate is determined by the market value of one's services. For instance, I may be able to charge $300/hr for general security consulting to a software vendor, but I cannot expect $300/hr for flipping burgers at a fast food place. It's contextual; there's not one price assigned to one person. If Charlie finds an exploit that could potentially cause a lot of damage, it's perfectly reasonable to expect the vendor to pay a value proportionate to that exploit's potential liability, damages, etc.
Hourly rates are determined based on market rates, and vary from job to job.
Hourly rates are determined based on market rates, and vary from job to job.