Context
It is the unit contribution: it serves as the basis for any other amount. You sell bonds in dollars and you receive pesos to the bid rate; The other way around, you pay for the sale.
As a historical reference: a week ago (06/11) US$ 1 cost $ 1.587,90 (-0,58%); a month ago, $ 1.539,70 (+2,53%); in the latter 30 days the range was of $ 1.536,00 a $ 1.588,60 (daily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.