Since you already have the Borla TD and test pipes, I'd go with Borla Headers ($575 parts and $300 labor), and JWT popcharger intake ($110 parts and $60 labor). That totals $1,045, just slightly more than your budget.
If I had $1,832 ($1,232 parts and $600 labor), I'd go with the Nismo R-Tune cams.
At some point you are going to need the Technosquare custom ECU flash. That's $595. But I would do that mod last, when I had all the rest of my N/A engine mods in place.
This can get expensive. Take it from one who knows.