Exhaust of your choice, ESS or Evolve Tune, Filter. This may be over budget and probably won't make more than 20 additional horsepower.
The main way to gain power is by removing the primary cats with a middle exhaust and software.
2014 White 911 C2S (On Order) | Leather Interior in Black | Sport Seats Plus | 7MT | PASM-Sport | Sport Chrono | PSE | Carrera S Wheels in Platinum | Bi-Xenon in Black w/ PDLS | Sport Design Front Fascia, Steering Wheel, & Mirrors | Burmester
2012 B8 Monsoon Grey Metallic Prestige Audi S4 | Titanium Package | AWE Exhaust w/ Resonated Downpipes | AWE S-Flo Intake | GIAC Performance Software