Have you played Cookie Clicker? A simple blend of active and passive resource acquisition methods can be intelligible and rewarding without taking a lot of time and attention on the part of the player. The addition of myriad upgrades can further deepen the earning process. Put something like that in the background of your game, where players can choose between scooping up money with their hands or running an enterprise on the side or robbing trains or something.

A couple games that come to mind that do money right are Recettear and, I think a couple of, the Assassin's Creed games. Recettear makes an entire game out of the merching aspect of economy, and has some sub mechanics with customer satisfaction and some top down action rpg aspects as well. Assassin's Creed did it with a property based system, where you would buy shops and buildings that would earn capital after a certain amount of real time had passed, and was integrated into other mechanics of the game.

Both kind of take the Idea of making a game or mechanic based around something real world of the time period. Merching (buying low, selling high) or playing with property. I think what Acharis says is pretty smart, the only games that have a real need for the money system to be fun is ones where it is a large, or the main gameplay mechanic (Recettear). Assassin's Creed's was good because it didn't interfere with gameplay, you set it up and let it run while you stabbed stuff.

So, I've been tossing some ideas back and forth in my head recently on how to make a game that requires you to get money to buy items in a fun way, rather than just beating the life out of enemies and having money drop from them.

Most games I have played seem to follow a very basic, and somewhat boring way of:

1. Kill a enemy, it drops some money, very common and while it isn't just handed to you it isn't that thrilling.

2. Doing Missions, this way may sound cool, but if the missions are cheesy then it becomes a real pain grinding them over and over.

3. Finding it in objects or lying around, this way isn't too bad, in the way it helps you show the player where to go. But it also makes it seem like the money isn't worth that much in the world.

Now, one idea I had would be something like this:

The player starts with a base amount of money from a “loan” of sorts at the start of each chapter of the story in the game, this amount will lower and increase depending on how much progress you make, and how well you do. If the player runs low on money before the next chapter, the player can get more in one of the following ways:

1. There is a mine shaft in a cave that is full of crystals, the crystals are used as money in the game. The player will get to head into it and explore the caverns and mine out the gems while fighting some cave creatures and avoiding hazards. It would be like a large level that expands through a huge cave system, with exits leading to connecting towns.

2. Another way to earn money is by going around and fighting enemies, like mentioned above. But they would drop it the gems rarely, but in large amounts. Making it not the best way, but it could help add that extra little bit of money.

The idea behind number one is to make getting money more entertaining, rather than feeling tacked on to missions or just dropped from enemies. But I am curious on what other ways could be done to make money collecting more fun in games.

The Shenmue games handled this well. There were 2 main ways to earn money in Shenmue:

• Acquire a part-time job: This was the most reliable way to earn money. You would play a skill-based mini-game for a few minutes and receive a reward based on your performance. This option costs the player time that they could have spent honing their martial arts or progressing the story.
• Gamble: This was a riskier way to earn money that cost less in time than the part-time job but carried the risk of losing money. The player would play a luck-based mini-game.