A single, powerful box (or a couple, for redundancy) may still be the right choice, depending on your product / service. Renting is arguably the most approachable option: you're outsourcing the most tedious parts + you can upgrade to a newer generation whenever it becomes operationally viable. You can add bucket storage or CDN without dramatically altering your architecture.

Early Google rejected big iron and built fault tolerance on top of commodity hardware. WhatsApp used to run their global operation employing only 50 engineering staff. Facebook ran on Apache+PHP (they even served index.php as plain text on one occasion). You can build enormous value through simple means.