My £4 a month server can handle 4.2M requests a day
People tend to severely underestimate how fast modern machines are and overestimate how much you need to spend on hardware.Back in my last startup, I was doing a crypto market intelligence website that subscribed to full trade & order book feeds from the top 10 exchanges.  It handled about 3K incoming messages/second (~260M per day), including all of the message parsing, order book update, processing, streaming to websocket connections on any connected client, and archival to PostGres for historical processing.  Total hardware required was 1 m4.large + 1 r5.large AWS instances, for a bit under $200/month, and the boxes would regularly run at about 50% CPU.