How much is the calligraphy of Qigong worth?

It's hard to say whether it's true or not. Modern people's simulation technology is extraordinary. You must get it from an expert and let him personally identify it for you, then you can argue whether it is true or not.

If it is genuine, and such a large banner can't be counted as 5 square feet per square foot, then it is at least 1.5 million at the current market price, but the premise must be genuine! If it is an original, I suggest you collect it without urgent need of money.