If there is non-numerical character in the data, it's being stored as a string, whereas only integers (or floating point numbers) can be summed.
To sum the data, you will need to:
- Create a preparation script
- Find and remove (i.e. replace with nothing) the dollar signs. Depending on exactly what is in the data, the "Extract number" processor may save a few clicks.
- Change the "Store as" to "Integer" by clicking on the column header.
Of course, the final output will no longer have dollar signs, but you can indicate the unit in the column header.