One for you off-road fans: last year's Dirt 4, which Andy enjoyed quite a lot, is currently the cheapest it's ever been right now. You can get it for $18/£13.50 from Steam. Before last month, it'd never even been below $20, so it's a good price.
It's on the accessible end of the spectrum and offers two different control systems—Gamer (ugh) and Simulation. Gamer gives you so many assists that it makes the game laughably easy, while Simulation turns most of them off for a more realistic challenge. Even then, it's less difficult than a lot of other racers, including Dirt Rally, the hardcore spin-off of the series (although you can manually play around with the settings to try to get the level just right).
So it might not be one for purists, but it's still a damn good racing game, marred by a slightly stale career mode. I always thought it was just too expensive to consider when it came out at $60/£45, but with the price at this level it's definitely tempting.
Dirt Rally itself is also on sale for the lower price of $12/£8, albeit for an older game (it came out in 2015). That's the one to go for if you're after a real challenge.
The deals only last for another 24 hours, so hurry over to Steam if you want to take advantage.