Go to Dragonsreach and look around.

Somewhere around there, there will be Whiterun Guads standing around, shooting targets.

They have infinite arrows, and don't mind if you take their arrows that they shoot at the target.

Now, take a bunch of the arrows off the target, then sell all the arrows to get gold (which are steel, I've done this before), and then repeat this process.
There is your infinite gold! (this can be done at any level, and I prefer going to the Riverwood shop, owner: that Lucan guy).