This sounds like a good candidate for a simple custom function. Below I have given you a sample. You would set this custom function as the "Function" of the virtual column and set the "Seed" to be the column with the gift amount.
If oField.ValueFor more information on how to create a custom function see http://www.omaticsoftware.com/Forum...fault.aspx
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Public Overrides Sub BeforeImport(ByVal Cancel As ImportOM.API.iCancel)
'Import has not been started yet