I have apr stage 1 and stage 1 carbonio and im extremely pleased by it. However i do have a downpipe coming in the mail to go stage 2 and its going to be awesome.
Would definitely go with the Carbonio intake stage 1+2. After that would be the APR downpipe and going to stage 2. This would present the most power gains.
If you are talking about cost effective then the cold air intake would be your next step.