For as long as I can remember using LibreOffice, I found that CSV files did not seem to be interpreted in a way such that monetary values preceded by a dollars sign (e.g. $12.34) would be interpreted as a numeric value. For example, when highlighting multiple numeric values, LibreOffice very conveniently shows the sum of the values in the lower-right area of the window.
The fix is simple. Check the box "Detect special numbers" as shown in the image below:
After this fix, LibreOffice very nicely formats any negative numbers in red ink.
Hurray! Now I'm all ready to analyse my 2015 expenditures!