I know my focus Ecoboost 182 will only gain around 20HP or about 11%. If I were to got the official route and use Mountune they also supply a new air box and intercooler but want £1k for it!Most cars won't get 50hp from just a remap. They might ask for that, but it won't actually run at that. If you dynoed it, it would probably be way short and get shorter as the engine got hot. It's like overclocking a CPU but not upgrading the cooler, fine until you put it under lots of stress.
Unless it's way over-engineered (e.g like a Supra or Skyline which can get huge power gains from the stock engine), but few modern cars are.