I find it funny that you think that $500k will cover everything that has transpired over the ENTIRE course of TDK viral. (And yes, I am very aware that this campaign has benefitted from quite a bit of freebies) This campaign has been active for well over a year. That does not include the pre-planning that this monstrous campaign needed. It wouldn't surprise me at all if the entire staff at 42 entertainment salaries alone are close to $500K a year. Three designers wouldn't cut it with what they are doing. They'd need programmers, along with designers who are very fluent to achieve the level of artwork with this campaign.
By your estimate, 42 Entertainment is doing this stuff for chump change if you ask me. I could see 42 Entertainment pocketing $500K gross profit on this deal, but there is no chance that it is that cheap to run a marketing campaign of this magnitude for that figure for over a year.
I don't doubt that 42e is working for considerably less than they deserve, but I do think that they are working for virtually nothing. When it comes down to it, most of the costs of this campaign are in payment of 42e's employees. Research tells me 42e employs about 50 people (and no doubt many more--actors, etc.--on a freelance basis--but for all I know, 42e employees are our actors [although I doubt that because when they can help it ARG creators seem to remain anonymous, and this has failed in doing so because it's the biggest one yet]), and they probably get paid utter crap. (One hopes they have job satisfaction.)
The question is of whether or not 42e is doing anything else concurrently, which is possible (they've done more simple viral campaigns that don't amount to ARGs), in which case, Warner Bros is probably not paying everyone a full year's salary.
But, say that they averaged out at $50k a year, which is not unreasonable although somewhat thankless--that's about $2.5 mil. The swag is relatively cheap, especially considering a lot of it--such as the free pizzas--is likely from WB's buddies so it's free. (The Dent stuff, though...wouldn't be...but they had that stuff produced en masse so it probably wasn't incredibly expensive.)
That's probably part of why viral campaigning is becoming more frequent and necessary--because it's effective, and people want something participatory, and best of all, it's dirt friggin cheap. The most brilliant part about viral marketing is that it gives you the most lusted-after kind of publicity these days--word of mouth. Perhaps lusted after because it officially costs $0 to have one person tell another person, "Oh man, did you check out ibelieveinharveydent.com? It's amazing!" If you've told anybody about this campaign, there you go. And look at how the numbers of people actively playing grow as time goes on...for the price of cheap and comped merchandise and a few virtual spaces (which anyone can tell you are inexpensive).
So again, the cost of this campaign is simply the cost of hiring 50 more full-time employees. Assume this comes out to maybe, I dunno, $2.5, $3 mill a year--even if you doubled it...$6 million would buy at MOST 12 30-second spots in primetime television and it generates astounding publicity considering if you turned it into time in TV spots it'd be about 3 minutes.