Context
With US$ 400 It is typical to make a monthly savings or separate silver for a trip: the difference between contributions is already seen in thousands of pesos. 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As a historical reference: a week ago (06/11) US$ 400 cost $ 635.160,00 (-0,58%); a month ago, $ 615.880,00 (+2,53%); in the latter 30 days the range was of $ 614.400,00 a $ 635.440,00 (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.