Brand Tailored Promotion Budget?

What comprises the "Budget" when doing a Brand Tailored Promotion? There is no charge, so not sure how that number works.

My assumption is that if I have a $100 product at 10% off through the promotion, a budget of $300 would mean I can sell 30 units before it ends (30 x $10 savings)

Do I have this right?

Cheers!

Ryan