I have many products that make more than $1000 a month. Tip - use the app stores to cut away the pain of having to market to users through vague means. App stores are a godsend if you are a good developer but bad marketer.
The app store for web apps is twitter and facebook.
Because that was the original question asked, as well as the topic here. Stay on topic, stay on topic.
"Is it hard to write a small piece of software and sell it over the web so I can make 1k per month to pay my bills"
"Is it hard to build, market and maintain a web app that makes at least $1000 a month? For a single, skilled web developer."
You might consider that splitting hairs, but I think the question was quite clear, and very precise. Basically, he's interested in capitalizing on an existing skill set and wondering about the business side of things.