While it's designed to cycle all your certificates every day, you can still configure it for weeks/months. It's also based on credentials rather than domain verification (shameless plug, I'm Anchor developer)
You're comparing engineer time to the wildcard cert transaction price. You're neglecting to include the time for dealing with the wildcard cert (including manually remembering to renew that).
With process automation, you (or better: a collaboratively supported tool) gets progressively better at nailing renewals.
JoshTriplett's "renew every 30 days, 60 days to fix the problem" approach strikes me as inspired.
Given a 90-day duration, set up automated renewal for every 30 days, and if that renewal fails, you'll have 60 days to deal with it.
With that said, still a big supporter of Let's Encrypt for folks who can tolerate the constraints.