They key (as someone who has done it) is to look for niche B2B opportunities. Find a need and fulfill it better or cheaper than existing players. Exploit newer/cheaper tech or SEO knowledge that the existing guys don't/can't get.
Think of it this way: you need 500 businesses to pay you $20/month to get to $10k/month. If you can get 1 signup a day, you're there in < 2 years.
One example: we run nextproof.com that lets wedding and portrait photographers sell prints online (think of it as a shopify for photographers). There are way bigger players in the market (pictage, smugmug, printroom, etc.) but we have ~2,000 users. Half of them are on a paid plan at between $9 and $99/month. The other half are on a free plan BUT we still make money on them through transaction fees. So, after 3 years, it's well over $10k/month.
Another option is premium content or tools targeted at these niche businesses. This could be in the form of WordPress themes/plugins, eBooks, DVDs, etc. We did an SEO DVD for photographers and sold 1,000 @ $79 each.
Most of the "ideas" I come up with are along these lines. I have tons of them.