This is a question to which you will have to answer yourself … The regulations of the 5th and 6th editions indicate that "there is a way to calculate income" but these are not rules, but suggestions.
This is an unfortunate example of "do what you want on the rules", but you may note that the companion's "active = annual income" mode is consistent with the 5th edition's basic rule book.
I also think that 5 times the annual income seems a bit too much. This might be realistic for higher class characters, not really for others.
If you want to run MoN, you can use the trick introduced when rewriting the campaign:
Jackson got a large sum of money (which is explained in the previous scenarios) and has a trust fund that he gives investigators in his will when they "continue his work ", making it a financial part of the investigators problem. questionable.
You can build around this idea to incorporate it into your environment (I do not think that managing physical resources should be a big problem in a CoC campaign, but you can of course do whatever you want).
S & # 39; fun!