Context
Small amounts like this are used to pay subscriptions, tips or make up a bill. You sell bonds in dollars and you receive pesos to bid rate; The other way around, you pay for the sale.
As a historical reference: a week ago (06/11) US$ 20 cost $ 31.758,00 (-0,58%); a month ago, $ 30.794,00 (+2,53%); in the latter 30 days the range was of $ 30.720,00 a $ 31.772,00 (daily sales data from ArgentinaDatos.com).
Keep in mind: It is legal and on the record. The actual price depends on the bond, the settlement period and your broker's fees.
The other way around? Passing pesos to MEP dollar.