I agree, New Relic's pricing model is almost too "enterprise". Per host pricing seems high, and difficult to scale. It's too bad, because I love everything else they offer. I'm even considering the new Insights service. I think they need to introduce a mid-tier pricing level between Free and Pro.
They've got a good foothold in the market as a all-in-one solution. I've attempted to find a drop-in replacement, without much luck. It's difficult to find a one-for-one service, but here's some similar services with entry-level pricing:
DataDog (https://www.datadoghq.com/pricing/): $15/host/month up to 100 hosts.
Scout (https://scoutapp.com/subscriptions): $10/host/month
CopperEgg (http://copperegg.com/pricing/): A la carte depending on service
Stackify (http://www.stackify.com/pricing/): $15/host/month
The biggest feature that I need is application level monitoring for PHP. There's plenty of great server monitoring tools, but not many services that track application performance like New Relic does.
I know there's plenty of ways to replicate New Relic, but who has the time?
Of course, I could be completely wrong, and missing a great alternative service.