Advice on what to charge for commission-based service (sponsorship "broker")

Hello Elpha members! I was asked to help a conference find corporate sponsors for an event happening next year. The employer asked me to provide an offer on what type of comission I would want on the sponsorship deals. I am to try to find 10 sponsors, each at 50K. Does anyone have any past experience or suggestion on what percentage of the sponsorship deals I should request?

Thank you!