* multi-language and accessible
* desktop, tablet, mobile -- doing this well requires pretty good design chops and a lot of testing
* handles money and credit cards, so requires PCI compliance -- there's little chance they're going to move to something like Stripe at their scale
* probably connects to a godawful homegrown inventory system
* very high uptime requirements
* integration with their analytics chain, to provide highly complex ad reporting and conversion optimization flows
* an administration UI that functions both at the global level and at the store level with complex permissions and reporting given the various management chains involved
Considering even a mid-tier dev costs order $200k fully loaded, a small front-end scrum team of 5 front end eng, a designer, and a PM runs you $1.4/year; a backend team of 10 also with a PM runs $2.5m. That's $8m over 2 years for a pretty small team and not super-expensive talent. I'd initially spec the Hertz site as over $20m to build. And that cost could easily rise.
I've told people who scoff at $32 million "for a website" that $32 million might actually be low, depending on requirements.