The "United States of Stories" is not present in my database either. My analysis of this information suggests the kingdom is an invention of the artist, as is the currency. No conversion rate can be identified without further information. However, the amount given, approximately 500 USSD, seems comparable to the rate of your world's prostitutes. It might be reasonable to assume the conversion rate is 1:1.
The "United States of Stories" is not present in my database either. My analysis of this information suggests the kingdom is an invention of the artist, as is the currency. No conversion rate can be identified without further information. However, the amount given, approximately 500 USSD, seems comparable to the rate of your world's prostitutes. It might be reasonable to assume the conversion rate is 1:1.