Howdy. First with regard to the data, use a dynamic named range, called DataRng:
=OFFSET(Sheet1!$A$1,0,0,COUNTA(Sheet1!$A:$A),COUNT A(Sheet1!$1:$1))
Now for the formula, you can use at least two approaches. This is the way I typically approach it. It adds an extra column, but not as intense later on. One is to add another column (perhaps to the left of the data, so that data can grow to right). Thus, your supplier is in Column B and Article in Column C. Then label that new column MyLU (in A1), and in A2 put this formula:
=B2&C2
copy down as far as data.
Define this as a named range (MyLU):
=OFFSET(Sheet1!$A$1,0,0,COUNTA(Sheet1!$A:$A),1)
And define name range Head:
=OFFSET(Sheet1!$A$1,0,0,1,COUNTA(Sheet1!$1:$1))
Then in a cell outside you range (X2 and X3), put the Suppliers for drop down in X2 and Article in X3, then in X4 put this formula:
=INDEX(DataRng,MATCH(X2&X3,MyLU,FALSE),MATCH("Pric e",Head,FALSE))