Air filters don't -always- need to be mapped in. It's not unheard of for a cone filter to cause issues for the car. Panel filters are much cheaper than induction kits. A filter on its own will give minimal power gains. Might get lucky and have 5 extra horses. Decat downpipe will give a moderate gain in power but 100% has to be mapped in to avoid fueling issues and overboost. Air filter, decat and a map could get you 20-40hp depending on other supporting mods.
I have a Cosworth panel filter, decat 3" turbo back and a remap. I went from 211hp to 276hp. I also had a RCM fuel pump and three port boost solenoid fitted for help and safety. Each car is unique in how it will take to different mods. It's never clear cut as this mod gives X amount of gain. Age, condition and type of fuel can also effect possible gains. Even the temperature 😂😅 Gotta make sure to close up all these loopholes.