AWS costs seem reasonable to me and it is definitely the smart way to build a service like this. Saves a ton on time early and services like this can optimize later when they are much larger.
My message to all startups out there: despite Valley folklore, it is ok to have a marketing budget and spend money to advertise to users - especially initially. Not every successful company or service grows "organically".
> it's expected to have payroll your largest expense - there was no surprise
Only when you are small haven't marketed the service and your subscriber numbers are still small. You could probably support 10x the subscribers with only 2x (or less) of an increase in staff.