Roll with the punches a little. Your audience will be happy for it. I can hear you saying. If you're offered a fee for your speech, refuse it. You're never going to get rich as a banquet speaker, and it is certainly a classy move to give back your stipend.
Most school systems operate under a tight athletic budget.
Your donation will be appreciated. Thank your hosts in writing Never neglect an opportunity to promote your own program by not thanking the people who were gracious enough to invite you in the first place. The coaching life is a constant promotion of the things that are dear to you. A gracious letter, repeating some of the kudos you offered out loud during your presentation, will become a treasured part of the season for all participants. Treat your invitation to speak at another school as a special thing.