Having worked at Uber for a number of years across Rides (2 sided marketplace), EATS (3 sided marketplace) and Freight (2 sided marketplace) I can help.

To build a successful 2 or 3 sided marketplace, the company has to build up the "supply" side before there is any demand. In the ride-sharing business, the supply, and limiting factor to grow, are the drivers. In the early days at Uber, Uber had to get enough drivers on the road so that when a rider requested, there would be a driver within a few minutes to create a good rider experience. The only way for Uber to do this was to "guarantee" earnings for the driver, whether they got rides or not. This looked something like, "we'll pay you $20 / hr to be online and accept trips when they come your way." Of course, this is expensive if you don't have a lot of demand.

However, once Uber was able to get drivers on the road and the word got out there on the rider side, riders had such a good experience that they would tell their friends, families, and colleagues about Uber, and demand for the product spread rapidly.

Can one build up a 2-sided marketplace without millions in investment? Possibly, especially now that many of the barriers to these kinds of "part-time" gigs have been broken down. You would need to devise a way that if a person or company is supply in your business, that they are making money elsewhere, and using your platform to supplement their business (Uber originally did this with black car companies). Then, as your business grows (likely slowly) they can move more and more of their business over to your platform, so you're not subsidizing the down time.

Happy to answer any additional questions about the marketplaces for Uber Rides, UberEATS, or Uber Freight!