Well it finally happened. rFactor 2 went on sale.

Until 23:59 EDT on 10/18/2015 the game is 40% off, which means in the US the lifetime version of rfactor 2 is $50.99. The standard version of rF2, which includes only one year of multiplayer access, is going at $26.39.
Since people who bought the standard version of rF2 will have to pay $12/yr for multiplayer after their one-year trial runs out, the lifetime version at this price pays for itself after 2 extra years instead of the usual ~3.5.
The rF2 devs claim all future official content for the game will be free, presumably for both standard and lifetime owners.

Assetto Corsa is also currently on sale at 30% off for another 5 hours or so from the time of this post, at $41.99 for the base game + both dlcs, which you'll need if you want to join the majority of servers.
In contrast to rF2, the AC devs will continue to charge for future dlcs. This may be a problem for some since you can't join servers running dlc cars that you haven't bought. There don't seem to be any plans to allow people who haven't purchased a dlc pack to join servers running it even if they wanted to drive a non-dlc car. This does mean that you will have to keep buying any new AC dlcs to be able to join a lot of mp servers, but multiplayer itself in AC is totally free once you buy the base game and some servers running only vanilla AC content do exist.

After these sales are over, rF2 will cost $84.99 for it's "lifetime" edition and AC+2 dlcs will cost $59.99.

If you were looking at buying only one, don't let some dweeb on the internet (me) sway your decision from one game to another and then get pissed at him (me) later if you regret it, but the general mood in the mumble-circlejerk at the moment seems to be leaning towards rF2. It's got a lot of the features that AC is missing (and has no plans to add in), that kept us from running OVGT3AC. So now that rF2's price is a little more reasonable, hopefully some day soon we can get a big ovg series or two going in it.

Anyway, AC can be found in the steam store, and here's the link to rF2 with the sale code already entered:
https://commerce.rfactor.net/purchase/select?offeringCode=40OCT15

If that link doesn't work, you can just click 'buy' on the regular rF2 website and enter the promo code 40OCT15.

EDIT: forgot to add that yes, rF2 is coming to steam in the "near future," whatever that means. I would imagine it might go on sale again when that happens, but apparently there isn't any benefit to waiting until that happens to buy it: http://rfactor.net/web/2015/10/14/rfactor-2-steam-release-information/

They also seem to be looking at eventually getting rid of the standard-to-lifetime version upgrade path (you'll still be able to buy either, just not go from standard to lifetime, I think), so if you're gonna get rF2 the lifetime version sounds like the better deal.