Personally, 3.5 Years of play, averaging 3hrs a day. Total of my occasional deposits averages out to $21 a month at the moment. My avatar and gear worth at least total deposits, but that is not the point. The enjoyment I get is worth far more than $21 a month, and that is the true value to me. That I could cash out my avatar is nice, but I have zero desire to do so.
From the variety of answers in this thread you can see that there as many ways to participate as they're are participants. Some (a very few) earn a RL living, although the cost of living varies greatly from place to place, and the investment of time and/or money involved is significant. Many more play without depositing, which is a real challenge in itself, but it surely can be done.
Most players deposit, either regularly or occasionally. The amount of those deposits varies greatly, but each of us can make the decision on what and when to deposit based on RL income and our desired level and style of game play.
A few choose to make investments into the game, sometimes massive investments. This involves both high levels of risk and knowledge, but should lead to the generation of real income if done wisely.
The path from never depositing to earning RL money is littered with failure, but as an astute trader it is quite possible. Personally, that sounds like a job, and I already have one of those, but for some the challenge and reward make it worthwhile.
In the end, it is what you make it. Make it something you enjoy for the price you are willing to pay, and get on with it. If there is no balance you can strike that is satisfying, move on or be miserable.
Miles