Possibly outgoing bandwidth. These costs are directly proportional to traffic and regularly 20-30x the unmetered rate for a colocated box
Obviously if you're growing your costs will grow, but that's basically a tautology. Bare metal costs also rise as you grow.
Except you're gonna need between 10 and 100 people to recreate the service in-house, not just one.
Trying to re-do something from scratch in-house is always more expensive than just buying the product.
while true; do
curl https://rails.app/do/the/thing
sleep 3600
done
The actual version is slightly larger because of error checking etc., but that's the gist. So that's one example of replacing (or rather: avoiding) a distributed system (an asynchronous job queue) with a small shell script.I don't mean to say that shell scripts always can replace more complex systems, but sometimes they're enough.