[PC] DOOM 64 - 1.99p @ CD Keys
Update (22nd March) - They've raised the price to £1.99. That's still cheaper than buying normally but obviously not as good as the price it was.
Just released on Friday for £3.99, CD Keys have DOOM 64 for 79p as part of the Doom Eternal Pre-Order DLC pack they're selling.
Redeems via the Bethesda Launcher.
* Please note that all prices are correct at the time of posting. However prices can vary quickly and significantly without warning.