You've probably heard of the concept of the Iron Triangle, also called the "good, cheap, fast" triangle. It revolves around the idea that for anything done in life, including software projects, you can pick only two indicators, and the third is sacrificed as a consequence. The answer to the question if you can build an app for free follows this concept closely. It may seem "free", but it won't actually be. Something will always be sacrificed in the process. You can try and develop it on your own, making it relatively cheap or even "free", but if you want it to have the bare minimum of quality expected of mobile apps in today's market, you'll have to sacrifice a lot of time. That time can work against you since the world of app development goes by so fast that new paradigms can surface during all that time, rendering your app obsolete very fast. So the short answer is no. You can take measures to make it less expensive with savvy business decisions, but making an app truly for free is not a feasible strategy, especially in today's market.