Look at the Mazdaspeed accessories for the Mazda3. It is well thought out and most of the parts can fit. Find out who makes the Cold Air Intake and the Catback Exhaust for instance, and then check to see if the same performance part under a different brand name costs you less. For instance, AEM has produced Mazdaspeed parts in the past with the Cold Air Intake. AEM sells this same part independent from Mazdaspeed. It may cost you less. Even if it does not you know the part works in the Mazda3 so you would not be experimenting with the other aspects of reliability. The Mazda3 is famous for throwing CEL check engine lights with this upgrade because the air fuel mixture has been improved beyond spec. The diagnostic on the computer registers a change/problem. The car must go into the dealership to get the CEL turned off. Some Cold Air intake parts are more aggressive like the Injen brand which may not harmonize as easily to your car's system. This is why I suggest that you use as a baseline Mazda parts. At least then you will have an informed opinion on exactly what can be done and maintain the reliability which is this car's forte. Good luck.
