The amount of $20 isn't relevant. What's relevant is how hard it is to come by $20 in the DPRK.
a) for people in the higher echelons of the party that are paid more (and might still be expensive to them), e.g. a 1% of the population
b) BS organised to give the impression that they are not behind, while in reality nobody can afford those, and the buyers are "actors".