Every Laravel Cloud Flex size hits its monthly cap at 672 awake hours, so scale to zero saves nothing once an app is awake more than 28 days a month.
Flex 512 MiB costs $0.04 of compute for 4 awake hours, $0.54 for 60 hours and $2.14 for 240 hours, and a Starter bill is the larger of $5 and your usage.
Schedulers, uptime monitors and steady queues keep an app awake, so check your own usage page before trusting a low-hours estimate.