One trick with this is to try to do it with as close to $0 as possible. Many apps fall into this category. Use the money for experiments, or to speed up things like data entry. Maybe for marketing or setting up a domain name.

And by trying to stick to $0, you tend to spot clever low cost marketing strategies that might actually be far more effective than putting $1000 on a Facebook ad. And you end up focusing on trying to get users right now rather than think in terms of runway, assets, and bloated features.

For example, we'd print out recipes and put them on some banners downtown, with link to our app for more.

Or we'd set up a fake blog and subscribe a domain name, with a single article that said "If You Are (target market), Here Are 5 Reasons You Must Download This App." It's shady but it brought in 3000 active users, who stuck around and shared it to their friends. The cost for that was around $100, including hiring a copywriter.

If you don't like apps, there's always something like dropshipping - be a middle man for two parties and make money off the arbitrage (which ironically scales well into an app). Some friends make a good sum collecting money for babysitters. One friend did a car rental business, but he got the cash up front first, then bought the car. Try to make it cost $0 where possible.