This is the reason I can't figure out how Uber or Lyft is worth billions of dollars. It doesn't seem like the barriers to entry are very significant. How long before there's an app that queries the different services and hails a ride from the service that can get there the fastest or provide the cheapest ride?
Except ride-sharing doesn't have a network effect. I don't care if all my friends use Uber; it makes no difference and we all will use the next company if they're even a dollar less / ride and the service quality is on par.
Drivers care that lots of people use Uber and you care that lots of drivers use Uber. So there's definitely a network effect. It's just a lot weaker than something like Facebook because I don't care how many Uber drivers there are in Memphis if I'm in Salt Lake City. It's even weaker than that because the geographic area is more like "within 10 minutes of me". You can see a competitor relatively easily getting a toe hold by starting service at a specific time for a specific area. For example, the popular bar street on Friday/Saturday nights.
The problem comes with your "a dollar less" caveat. You star EpicEng's ride share and undercut Uber/Lyft by a dollar. They respond by matching your price and giving drivers more incentives so they don't switch. Now what do you do?
I can assure you that I do not personally care that people use Uber, but that's neither here nor there. What you describe is not a network effect; it's true of _any_ business you want to see stay in business. If I liked shopping at e.g. Walmart, yes, I would implicitely want others to shop there as I don't want to see them go out of business. That doesn't mean I'd have a second thought about switching to a competitor if they provided a similar service at a lower price.
FB is successful because no one I interact with is on a different platform. They same is true for them, so we all stay. Network effect.
It's not network effects so much as the strength of the two-sided market they've created. Installing an app and registering is a lot of friction. On either side you'll probably bother doing so for no more than one or two services, which in most situations will cover most of whatever market exists.
But in general the answer is either having a disruptive strategy or else a huge amount of money to woo existing market participants. Most of us don't have either. That's the barrier to entry.
