My cd player may not work in my 2004 accord, it is working so far but has gave me the mechanical error once already.

I don't plan on paying 700 for a cd player nor 250 bucks at the moment for a used one.

I figured I could use Honda's AUX input and add me a cd changer to the thing and put it in the trunk or whatever. I could even use a MP3 player which would be just fine.

But there is no aux input, just a option. I guess I need some sorta adapter to use the AUX input?

 

yes, look at Pacific Accessory Corporation or USAspec for factory interface adapters.

you could also add a new CD player in the pocket below the factory radio (a very common solution and they make kits for it).

 

I have a Pac Audio adapter on the back of the radio so I can use subwoofers. Can I still use one of their adapters so I can have inputs?

 

sure, no reason you can't use multiple adapters that do different things.