How to Account for "-" in Excel

I have been working on an excel document where I'm essentially just adding up costs for a made up company. I want to make it so that I can track the differences from year to year. For a some cells, this isn't a problem, as most of them have numerical values inputted in them. However, for cells that have no cost associated with them, I have put "-" to fill the cell. This is because, while some cells have "0" inputted in them, this 0 is meant to represent a value under 50,000 (as each cell has a value that is meant to be read in the millions). To try to get around this problem, I have been fiddling around with IF, OR and AND statements to try to tell excel to do different things depending on which cells are filled with what. There are three problematic cases: (1) when the first year I'm evaluating has a "-" in a cell and the second has a numerical value; (2) the inverse of (1); (3) when both years have "-" values. The third one I have solved separately by just putting:

    IF(AND(ISTEXT(N3), ISTEXT(D3), "-", N3_D3))

However, I can't seem to be able to add solutions to problems (1) and (2). Any advice on the matter would be greatly appreciated. Thanks in advance.