The Eastern Region network's official day is 05:30–23:30 — six dead hours nightly. A red-eye landing has no bus however regular the timetable looks, and the app-car driver pool thins in the small hours.
KFIA publishes no taxi tariff; the figure is set at the desk for the destination you name and paid before boarding. Fares you read elsewhere (SAR 85, SAR 70–110…) are other travellers' quotes, not your price. VAT (15%) can be quoted off the top after the desk number, too.
The airport states only licensed operators may pick up passengers at KFIA, and their desks are the last thing between the arrivals hall and the kerb. An offer of a lift made to you in the corridor, away from the Ground Transportation Centre, is unlicensed — and the 'SAR 60 to Khobar' it comes with is not enforceable.
King Fahd sits 31 km (about 40+ min) northwest of downtown Dammam across one of the world's largest airport sites — the drive from the terminal to the highway alone eats real time. Business travellers under-estimate the margin before a morning meeting or an onward Causeway run.