Provide advice on statistical method for transaction data analysis

I am looking for someone with good knowledge of statistical analysis to provide consulting on a data analysis problem. I am writing a small application to analyse exported transactions from a bank account to calculate average monthly totals of income and expenses. The challenge is that it should use statistical methods to determine if there are transactions that are once-off outliers which should not be included in the analysis to determine the monthly averages. I am looking for someone who can provide advice on a suitable method for doing this, explain the detail to a level where I can develop the code, and assist in determining whether the code is working correctly by providing test data/results. Alternatively, if you also know Java, I would be happy to award you the work to write the algorithm and test cases in code. I have a 1st-year university understanding of statistics (from a few years ago). Please provide good detail in your response to help me judge the most suitable person to award this to. Template responses will be ignored.