Does anyone know how much a square foot is for calligraphy and painting by contemporary painters?

As far as I know, if Mr. Fang Zhu Sheng's handwriting is an ordinary transaction, at least one painting costs about 30,000 yuan, and of course it depends on several square meters. If it is a tour or an auction, it will cost 800,000 yuan. My family has relatives in the painting and calligraphy association. It is suggested that the handwriting of Mr. Zhu Sheng, the collector, is more cost-effective, because it will increase a lot in the next 1 3 years.