as said, filter, exhaust and remap will get the easy power gain of about 8bhp lol.
after that you got to work for it. cams and airbox, or ITBs, or Turbo/SC depending on budget.
probably better keeping the engine fairly standard and investing in lightening it, or uprating brakes, tyres, wheels etc.
GDi havent released prices, or any power figures on their ITB kit yet but it runs off an omex iirc so budget over £1k just for that part.
you could DIY the throttle bodies tbf, jenvey sf's, clear a route by lowering rad, swap to manual throttle not dbw but nothing comes cheap