However, you have the added complexity of needing to thank these donors for attending the end of year Gala as well.
Here is an example to give you an idea of what this thank you note could look like:
This is just a quick note to say "thank you" for your continued support of (our organization). Without your contribution, and ones like it, it would be impossible to (do the function of our organization).
Your donation of $2000 will be put towards... (state a specific function that the money could be used for. This will help the donor visualize how his contribution can be used.)
I also want to thank you for attending the end of year gala. We know our sponsors are very busy people, but we cherish the opportunity to show our appreciation, and the end of year gala gives us that opportunity.
So again, thank you so much for your support. May you have a happy and prosperous year.
Sincerely, (Your Name)
When you thank someone for attending an event, you're basically thanking them for a time investment.
Bt noting the fact that the donor is a busy person, you're acknowledging that time investment, even though the event is something that you host in order to thank the shareholders.