CalculatePriceDailyImport.cs

public List<List<string>> FetchPrices()
{
    var priceData = DB.LoadPriceData();
    var parsed = new List<List<string>>();

    var costPriceField = 5;
    foreach (var row in priceData)
    {
        var price = row.Value;
        parsed.Add(new List<string>
        {
            BuildProductSku(price),
            CalculatePrice(price[costPriceField]).ToString(),
            price[costPriceField].ToString(),
        });
    }

    return parsed;
}

CalculatePriceFullImport.cs

public (List<List<string>>, List<string>) Parse(IDictionary<string, List<string>> dbData, 
    IDictionary<string, List<string>> csvData, IDictionary<string, List<decimal>> prices)
{
    var parsedData = new List<List<string>>();
    var skipped = new List<string>();
    var skuField = 3;
    var costPriceField = 5;
    foreach (var line in dbData)
    {
        var product = line.Value;
        if (!Validate(product, csvData))
        {
            skipped.Add(product[skuField]);
            continue;
        }

        var parsed = product.Clone();
        var price = CalculatePrice(prices[product[skuField]][costPriceField]);

        parsed[8] = AddEnvironmentalFee(price);
        parsedData.Add((List<string>) parsed);
    }

    return (
        parsedData,
        skipped
    );
}

CalculatePriceNew.cs

public decimal CalculatePrice(decimal costprice)
{
    var price = costprice / (100 - Margin) * 100;
    return AddEnvironmentalFee(ApplyTax(price));
}

CalculatePriceOld.cs

public decimal CalculatePrice(decimal costprice)
{
    var price = costprice / (100 - Margin) * 100;
    return ApplyTax(price);
}