To begin to estimate the rate of return on your investment, you must first calculate the current cost of the tasks you plan to automate. Then, estimate the cost of the tasks under the proposed system.
Determine these numbers per year. Next, get an estimate on the costs of automation and subtract that from the cost of current tasks you plan to automate. From here, you can get the rate of return on your investment. This is a high-level cost justification and should be analyzed thoroughly to get an accurate cost justification. Remember, some costs based on this analysis could be justified as "soft" benefits and can not be placed a dollar value. These "soft" benefits are intangible benefits such as increased efficiency, increased information accuracy, improved sales, and increased customer satisfaction.