Something like
* Users 1-2,500: $0.01/user
* Users 2,501-20,000: $0.0625/user
* Users 20,001-80,000: $0.0583/user
might be a tad more intuitive, especially if you listed the top-end price along with that.
For analytics, simple tiers (without pro rating) should work fine.
Someone below said that you should base your pricing on cost - I completely disagree. You should absolutely NOT look at cost when you put pricing together - rather, you need to ask your customers about the value of what it is you're providing. For example, Heap will be saving the time and hassle of deploying a generic solution on a server and the time of customising it. Plus Heap will be improving their product every day whereas the self-hosted version would need a developer to add new features. These sort of things all add up - you'll be surprised what you find out when you ask your customers.
Pricing is hard. There are a lot of good articles and discussions on HN if you do a bit of searching.
Good luck. Heap looks good