Well, you have to be prepared to offer some skill or talent to people, or at least provide a service that other people don't want to do for themselves.

I myself have started a business doing airbrushing and silkscreening on T-shirts, which has a very low investment cost (under $500).

The only home based business I can think of that has NO start up investment costs would be a research business. Basically, this could be using the internet to do research for people, or could involve clipping newspaper and magazine articles out for clients. A client would hire you to look up everything you could on say, bicycling in New York city, and you would provide them with newspaper articles, magazines, websites, book titles, etc.

This could also include something such as clipping out pictures as well. Many people could use pictures of let's say, animals..but also practically any other image you can think of. Artists, libraries, Advertising people, photographers, etc are always looking for images. Pick up some National Geographic magazines out of the garbage or at a garage sale, take a pair of scissors and start clipping pictures out and filing them according to category (Aardvarks, Apes, Artifacts, etc.) Artists call this a 'Photo Morgue', and these things are available at your local (reference) library, too. It's true that Google image search does much the same thing, but there is no comparison of the quality of a magazine photo and one ripped from the internet (not to mention copyright violations).

I came across a book once, called '100 home based businesses you can start on a shoe-string budget'. Some of the ideas in this book were truly innovative, and I watched as other people started them up themselves and turned them into a profitable home-based business. The 'research based' idea above was in this book. One of the other ideas was making wire trash-baskets at home, then selling the ADVERTISING space on the sides of them. There never seems to be enough trash baskets around in any urban environment, and you don't need anyone's permission (such as the city) to put a trash basket somewhere.

Advertising is huge business. Many companies will pay you pretty well if you can think of an innovative way to advertise their product for them. Any money spent on advertising is also tax deductible. This is how (and why) you can make money by making wire trash baskets. There was a punker in New York City that used to charge people (Advertisers) $1000 a month to have their ad shaved into the back of his head. You might have seen him in a Volkswagen commercial.

Selling products through word of mouth is a relic from traveling salesmen in the 1930's...

it's not a legitimate / modern / efficient distribution system... Not in the age of global shipping and the internet- where anyone can find anything they possibly want.

As a professional work-at-home marketer, I would be exceedingly cautious about joining any kind of "word of mouth" or network marketing system.

Don't get into a field where 90%+ of the programs are basically scams, even if there are a few good ones.

Get into a more modern, future-oriented kind of marketing.