Power Query / DAX equivalent to Excel's Index Match with Dynamic Array

Ok emcalleja , try this. And I apologize if I mangle the field meanings due to them being in not English. 😂

This measure works I think.

Price = 
VAR varCurrentDate =
    MAX( Salidas[Fecha de movimiento] )
VAR varCurrentItem =
    MAX( Salidas[Nombre] )
VAR varEntradasData =
    FILTER(
        Entradas,
        Entradas[Nombre] = varCurrentItem
            && Entradas[Fecha de movimiento] <= varCurrentDate
    )
VAR varEntradasMaxDate =
    MAXX(
        varEntradasData,
        [Fecha de movimiento]
    )
VAR varPrice =
    MAXX(
        FILTER(
            varEntradasData,
            [Fecha de movimiento] = varEntradasMaxDate
        ),
        [Costo / Venta]
    )
RETURN
    varPrice

The problem is you need a bit of modeling. See my PBIX. file. It returns this:

Here is what I did

1. I got all of the names (nombres?) from both tables and put them in a Names table, then removed duplicates. The problem is you have some case sensitivity issues, so I had to change case to "proper" because to Power Query, Car <> CAR <> CaR. DAX doesn't care. Power Query does.
2. I used hte Name table as my 1-many in the relationship shown here:
   1. 

       

3. Then I created and used that measure in the table visual above. I am pretty sure this can be optimized, but shoudl get you started.