U can get in Sofitel Complex, there are lots of PC shops around.
80 Gb 2.5inch SATA costs 225 riyals.
250 Gb SATA 3.5 costs around 280 QR.
500 GB SATA 3.5 costs around 450 - 520 QR

I think for PS3 u need USB HDD and not SATA.
IF usb, best u can go for Western Digital 500Gb for 460 riyals.