will buying a cheap intake on ebay and putting in a good k&N filter have the same effects as a aem or injen

sure why not

^ what he said

It's all similer, like they said above. Unless you need the CARB exemption, the paying the extra $$ for an AEM or injen ins't really neccassary. A CAI works, because for every 11.1 degree's you lower the intake temp, you get a 1% gain in HP. The filter also plays a big part. AEM and Injen have good filters. If you are running a K & N filter, that is a very good filter, so that will be fine. The piping will be similer. The output gain will really be similer. Running a custom set-up like that, the difference is HP will have more to do with the ambient outside temp than it would not having an AEM. Unless you need thw CARB exemption (meaning you live in Cali), just get the custom one w/ a K & N. The piping should be the same size and similer, and you'll have a qaulity filter. Like I said, it's mostly the same in this regard, just no CARB exmeption if you live in cali.