Well...you are requesting one column from your DB:
runQurey("SELECT Price FROM Products WHERE ProductID = 1");
And then trying to process two columns:
lblprice.Text = cusReader.GetValue(0).ToString();
lblquantity.Text = cusReader.GetValue(1).ToString();
I suspect you want to return more columns, so try something like:
runQurey("SELECT Price, Quantity FROM Products WHERE ProductID = 1");