just to add a slight correction, it was my old type r that had ap's, my current car is on brembo's with uprated pads, and given the extra weight between the two they are a bit meh, bear in mind i am running 380/390 and aiming higher and even on a road car the current setup just wont be up to it.
price isn't as much as you think,
https://www.godspeedbrakes.co.uk/impreza-1993-1998-wrx/218-impreza-classic-newage-wrx-ap-6-pot-330mm-kit-.html £1700
https://www.godspeedbrakes.co.uk/impreza-1993-1998-wrx/292-subaru-impreza-ap-6-pot-355mm-kit-.html £1800
although it isn't with proper AP disks. Given the power levels being talked about, i expect the 330mm kit will be plenty although your only talking £100 difference i'd personally go for the larger ones anyway (check wheel fitment), RCM do em at £2500 for 355 kit.
alcon kit is slightly cheaper.
https://rogerclarkmotorsport.co.uk/store/product/732-rcm-alcon-6-pot-front-brake-kit-black-343mm £2200
tbh its something i wanna look into as its on my to buy list.