How much? I'd say 50M$ would be adequate.
2 adverts for reddit merchandise,
1 reddit flash game,
1 advert for reddit gold,
1 for a subreddit,
1 "thanks for not using adblock",
1 for the reddit ad system,
1 for a conference called poptech
and then on 3 pages I saw "sponsored links".
Since the community is less vigilant than it used to, I assume that the newcomers are less concerned about commerce.