Then that becomes part of your business + technology planning conversations:

"This is the cost of scaling, this is the cost of owning our own infra, how does that fit into our budgeting and requirements?"

"If you can't afford it" is doing a lot of assuming and a lot of heavy lifting in that statement. Whether or not you can afford it depends strongly on your scaling bounds (how much you need to scale) and how you've chosen to implement it.

There are plenty of tools and systems that can present a sufficiently linear cost relationship to load and usage that, should your COGS versus revenue make sense, the marginal cost of increased cloud resources a no-brainer--especially versus always-paid-for hardware. If you don't have such a linear relationship you're as much in the position of deciding whether the project is viable as you are anything else.