Does that include my own salary?
Although I am doing an educated guess, I think that your NDA mentions "prices, costs, business affairs,..." to refer about the prices and costs of your products and services, as well as the business partners and customers your company may have.
This includes, but may not be limited to, the price you charge to each client, the internal costs and prices of the materials you use or the products you create, the margin of profit you are obtaining, etc.
This has no reason why to include your salary, as you are no product or service of the company (technically you are an asset, but still a Human Being after all).
Mentioning your salary, although not recommended, is sometimes required when applying to jobs (specially in the application forms one may fill), so it is a common or at least not rare question to be asked.