I have designed and about to complete the development of a unique messenger app that is applicable to the global market that solves a very common problem. The app is monetized through PAYG and subscriptions. I am in the process of creating an explanatory video to assist with the marketing. I am a sole founder based in South Africa.
Good luck with you venture!
You basically have two options. Funded vs. bootstrapped mode. Assuming you are not going to look for investment for this particular project, your other option is to bootstrap.
Bootstrapping is becoming more and more popular nowadays, since it lets you gauge the reaction of the market very early. I recommend following Pieter Levels about this on Twitter and other media.
And I suggest watching this is a generally working - good model of how to launch a product: https://www.youtube.com/watch?v=6reLWfFNer0