It's sort of close, but we're still talking about a swing of >30% there -- $5 billion dollars in WhatsApp's case.
There are many things missing from "cost per user" but I think the first thing to ask is "user doing what"?
"User doing what?" is a decent start. But of course, we have a host of other considerations to ponder: technology, platform, integrations, competitive blocking and tackling, etc.
FWIW, I still can't wholly grok the WA purchase price. The price seems largely to have been driven by competitive bidding between FB and Google. Also a healthy sprinkling of defensiveness and fear, mixed with a dollop of "because we can." Factor in some "we believe our stock is overvalued, and as such, we will realize a discount on price correction," and I suppose you arrive at a figure that will end up south of FB's nominal purchase price. The one thing I can say is that Instagram looks likes a ridiculous bargain in retrospect, and especially in comparison.
That said, to whatever extent we do want to talk about user counts, it's worth noting some history. Around the time Facebook had an estimated $15 billion valuation, on the heels of Microsoft's advertising partnership/investment in 2007, Facebook had about 50 million active users. WhatsApp has 465M+. Apples and oranges, to some extent. But still. Worth considering.
I'd forgotten completely about YouTube. At under $2B, that must have been one of the best acquisitions of the whole bunch.
YouTube for 1/10 the cost of WhatsApp.
I tend to think more about acquisitions as capital per employee, as in, that's how efficient they are at creating value. It's more interesting that comparing users because of the "users doing what" question. I'm disappointed i can't find graphs about those. Last companies I checked (but I can't remember which ones), the capital was around $1m per employee. Except for WhatsApp.
When was the last time you paid Google for search results? Meh, can't be making that much money.
Nice way to show I was wrong :)
If our patience is worth any money, Youtube is extracting it in spades now.