Returns the value of CostValues attribute. This attribute represents component costs for which the total cost for the cost item is calculated, and then multiplied by the total CostQuantities if provided. If CostQuantities is provided then values indicate unit costs, otherwise values indicate total costs. For calculation purposes, the cost values may be directly added unless they have qualifications. Cost values with qualifications (e.g. IfcCostValue.ApplicableDate, IfcCostValue.FixedUntilDate) should be excluded from such calculation if they do not apply.