I'm finding making money too easy.

I find freelance programming to be the one that takes the slowest to earn money with if you're looking for a non-career option. Yes some of the later stuff can earn you a bunch of money but it usually takes longer to do and you need a higher programming level to do it (creating video games can take quite a while) and you can always limit your sims to doing the lower level stuff if you don't want them to earn money too quickly.