Dear _______________

Your offer of help is truly appreciated at this time. I believe if we can get our cost estimates down, we should be able to have this proposal ready to submit by the _______________ (date) deadline.

I know that by taking you up on your kind offer, we will both be burning the midnight oil for the next week and a half, but I really doubt that I will be able to complete this within the time limit without your help.

Thank you very much.