Money Money Money!!

The most realistical answer is to be a contributor from now on, upload your quality work everyday, and get them approved. Than you will know the answer eventually. 

I suspect there are a handful of contributors who have been participating for years and who have thousands of marketable and in demand assets that might be pulling in that much a month, but the vast majority aren't coming anywhere close to that figure and consider this a side hustle to make a few extra dollars in spending money. And the competition gets tougher every day of the week, 24/7. Since the royalties for videos are higher, such contributors might be meeting such a goal or better. Compared to others with 10,000, 20,000 or even thousands more, your 1000 assets are among starts in the night. 😉

How do you expect us to answer your question? That depends on how many images you sell, what kind of license is sold, what the buyer has for a subscription, the quality of your asset, the quallity of your metadata, the number of assets in your portfolio and the demand for your assets.