If you email jj@rootly.com we can get you some pricing ASAP. It'll be dependent on number of users and level of support/onboarding/custom feature development required.
But if you're a small team, Rootly is powerful and ready to go out of the box with defaults and you might not require some of the custom stuff.
To answer your question directly, we customize each package for each individual customer on a bunch of variables.
Building a calculator that lets potential customers input their variables and you show what the pricing would do solves that problem fully, and takes minimal amount of time to implement.
That you haven't spent that short amount of time in order to be transparent, looks shady to me (and others, some of them even write the same in this comment thread), as otherwise you'd surely display your pricing upfront.
Actually we did offer a free plan for up to 5 users and even 10 at one point. What we've found is the collaboration overhead during incidents at companies at that scale wasn't too useful and pivoted away. Instead we offer a 14-day trial so customers can get their feet wet without contacting us: https://rootly.com/users/sign_up.
For the vast majority of your users, I would expect the amount of installation-engineering required to be zero. For every big business on an Enterprise plan of a SaaS like e.g. Cloudflare, there are 10 or 20 accounts for customers just as big(!) who are on their Business plan — which is basically the same feature-set, but without any of the high-touch custom stuff. Because they don't need any of it, in order to get all the value they need from the SaaS.
In other words, it feels like you have an Enterprise plan, but no Business plan. It's pretty easy to construct one — just assume any high-touch stuff doesn't happen. What's the base cost, per user?