How can I add a price range and make my num1 depend on price range in my Code?

How can I add a price range in my code and make " num1 " depended on the price range ! I want to assign some specific values to price range and then make my num1 to fetch that value ! Eg 1.if price range is (1 to 1000) then num1 = 10 ... 2.if price range is (1000 to 2000) then num1 = 20 ...

My Code :

        int num1 = Convert.ToInt32(Price.Text);
        int num2 = Convert.ToInt32(DropDownList1.SelectedValue);
        int num3 = Convert.ToInt32(DropDownList2.SelectedValue);
        int tax;
       
        int petrol;
        int cng;
        int diesel;
        int personal;
        int commercial;

        petrol = 1000;
        cng = 2000;
        diesel = 3000;
        personal = 500;
        commercial = 700;
        tax = 0;

        if (DropDownList1.SelectedValue == "1" | DropDownList2.SelectedValue == "1" )
        {
                tax = num1 + petrol + personal;
        }
        else if (DropDownList1.SelectedValue == "2" | DropDownList2.SelectedValue == "1" )
        {
                tax = num1 + cng + personal;
        }
        else if (DropDownList1.SelectedValue == "3" | DropDownList2.SelectedValue == "1" )
        {
                tax = num1 + diesel + personal;
        }
        else
        {

        }
            
        if (DropDownList1.SelectedValue == "1" | DropDownList2.SelectedValue == "2" )
        {
                tax = num1 + petrol + commercial;
        }
        else if (DropDownList1.SelectedValue == "2" | DropDownList2.SelectedValue == "2" )
        {
                tax = num1 + cng + commercial;
        }
        else if (DropDownList1.SelectedValue == "3" | DropDownList2.SelectedValue == "2" )
        {
                tax = num1 + diesel + commercial;
        }
        else
        {

        }

        CalTax.Text = tax.ToString();