As a senior developer/architect in a small company focused on MS web apps. I estimate that we could do something similar to the CB for about $250K to $300K. Maintenance on it would run up around 100K annual, if you wanted to do a decent job of tech support. You'd need a higher rate at start up for a few months. If you wanted it done really fast, those costs would go up sharply. We've done comparable or even larger things over a two year period, and met those rates, though.
OTOH, our company is in an area with a lot better cost of living than Seattle. Not sure what the factor would be for that, but double wouldn't surprise me.
Server costs aren't peanuts, but they are fraction of the development costs and tech support/maintenance employee costs.
None of this takes into account the non-technical people involved (publishing content) or any cost overruns from people not knowing what they were doing early.
So, not sure how profitable the whole thing is, but I'd say if they are pulling $400K to $560K per month, they are well on the road to profitablitlity, and it should get gradually better as time passes, initial investments are regained, and lessons are applied.