Yes, it is possible to see the wall from Beijing to Shanghai within three days. On the first day, you take a flight from Shanghai to Beijing. The flight journey will take about two hours. And when you arrive in Beijing, find a hotel to lodge in and have a rest. On the second, you can spend half or near one day to visit the Great Wall (for example Badaling). And on the last day, go back to Shanghai.

How much does it cost to fly from Shanghai to Bejiing in US dollars
value? Someone said 40 in China currency - how does that translate?

40？No, Shanghai to Beijing flights cost more than 1000RMB. Recently, the cheapest should be 164USD (1110RMB). Few midnight flight may be cheaper a little.