I wasn't aware there were adjustable difficulty settings in the first place.
To be honest I didn't ever really find the money situation to be an issue - surprisingly, since I'm not good at games in general (not awful either... just average). I guess this just suits my strengths. I was never near running into money issues at any point, like, here's an example of my 'save tree' for the first few days if you like:
The main thing is to be accurate. You want to be quick, but no point rushing if it means you make errors all the time - accuracy is more important. You get quicker as you get used to the interface, anyway. And if you read all the pages of the paper every day (you can do that before starting; doesn't take any time) you can get it all straight in your head before a timer even starts.