The finances are on pages 12 and 13. The short version: they're spending money on all the things you'd expect, but they seem to be slightly cash flow positive and have accrued around $100m in net assets.
The usual "economic justification" for such things is that people are paying it.
In reality, very few people pay the individual article prices. The real market is in site licensing, as it were. The individual article prices are probably set to support the sales story on these institutional access licenses, not the other way around.
I think you can also get access to the ACM library via membership. When I was in college I paid for a student membership, I think its was $25/year or something generally reasonable. Probably a better value proposition than my actual CS degree, not that its a great point for comparison.
That's true. Many of these sorts of memberships are at least a few hundred dollars when you are no longer a student, so they add up pretty quickly (but maybe have tax credits).
