Generally the elastic or usage/volumetric type billing structures are used on SaaS/cloud products, not on-prem.
Although it's entirely possible that elasticsearch, and other vendors in the space use that pricing model for their on-prem customers.
Regardless, that's even more of a reason why it would be very difficult to give a quote without being first having a presales meeting with a solution architect or knowledgeable rep.
We're not talking about some punch card COBOL machine he jimmy rigged with network access, it's an old Debian Linux box with SSH enabled.
It's not like Metasploit would have a tough time finding unpatched vulnerabilities for it...