Pro licensing, which has no limit on the number of domains or accounts is $20 per month per VM. I target 250 accounts, each of which has ~3 domains on average. At that point your per domain unit cost is $0.02 per domain per month or less. If you were to go with a Startup license that has a domain cap of 50, then your per domain cost is $0.08 per domain month.
As a rule of thumb I recommend building out 250-300 accounts on a 16-24 GB VM. You’ve enough slack to handle surges and distribute your risk across multiple servers. Node failures happen. 
The magic comes once you price out third-party licenses that are core features of ApisCP.
- Softaculous ($1.50/month) already built into ApisCP’s Web App module, which launched Update Assurance yesterday. UA performs stepwise content-length and HTTP status checks during updates, rolling back if aberrations are noted.
- CloudLinux ($14/month) already built into ApisCP. All accounts are jailed to synthetic roots, a feature of ApisCP since its birth in 2002. Resource enforcement, just like in CloudLinux, is powered by cgroups - a native kernel feature.
- Immunify360 ($45/month) Malware scrubs, DDoS prevention are managed through Rampart in ApisCP. A mod_security hook filters file uploads and sends an alert to block offending IPs.
- MailChannels ($69/month) - or any smart-host. If you have enough servers and enough diversity in mail, ApisCP can communicate over an rspamd cluster that provides excellent spam mitigation. Clustering is a turnkey feature in Bootstrapper. Set
rspamd_redis_serveras part of mail/rspamd.
$20 per month versus $1.50 + $14 + $45 + $69/n = $129 + BYOL ($???), $20/month is a steal for the features you get. All of these components are integrated with precision; there’s less noise and fewer remarkable events because everything is vetted by real world testing through my hosting business as well. 