Right, but take Mossad, a well-funded intelligence agency. Their annual budget is estimated to be about $2.73bn[0] ... how much do you think Big Tech spend on cyber-security?
In total? Maybe an order of magnitude more - so across all of Big Tech, in all projects and ongoing maintenance activities that are directly enabling or powering their cybersecurity aspects... I'd say $25B. Altogether.
Let's look at the other side of the equation and see what they are up against.
Now, obviously Mossad won't be spending all of their $2B on offensive stuff in this space, but on a ballpark estimate I'd say their spend on offensive cyber[tm] is between $300M and $500M.
From vulnerability equity programs we know that the going rate to acquire a reliable exploit against a high-value, hard target is between $1M and $3M. So we can safely infer that it would cost at least that much to develop one from scratch. Let's be charitable and say that on average it costs around $2M to develop a bespoke exploit against a hardened, niche target. These exploits also have their shelf-life and will eventually get burned. Again, we can be charitable and say that on average an exploit remains useful for maybe 18 months. Over that time the adversaries will either have developed their own parallel methods, or will be buying another one to replace their now-expired product.
That puts the expense floor, before operation staffing costs, to somewhere around $750k per year just to stay in place with regards to access technology. For high-value, bespoke targets where no exploits are readily available from the brokers, you can still expect to spend about $2M per year to develop and maintain a matching capability.
Then let's consider the operation personnel costs. A well run intelligence operation is probably not a sweatshop. With our venerable Stetson-Harrison estimation method we can put an average headcount per operation to 9 people. An operation lead, two analysts, three software engineers, one project manager, and two support staff. Let's say the fully loaded cost for lead and manager is $300k each, for software engineers $250k each, and for analysts/support $190k each.
So a single operation could expect to have annual, ongoing costs just a hair under $4M. Around half for maintaining the access technology and the rest to keep the operation going. Let's also say that the intelligence agency maintains a discretionary buffer budget to absorb occasional one-off cost runs, so that if a project for some reason generates an extra $1.5M charge in one year, it'll be expected slippage and already accounted for.
At $4M per year, per project, and a minimum of $300M to spend on such projects, you can maintain a lot of access operations. For just one intelligence agency.
When I said that nation state adversaries have effectively unlimited budgets, I meant that they can keep paying those sums just to maintain their access. For them, the ongoing access itself is an essential means to an end. They don't attack systems because they need to get through a system. They do that to achieve their objectives. Those are not "breach systems X and Y" - they are more along the lines of "collect and exfiltrate information of type M". How they do that is irrelevant. And as long as they can maintain their access to relevant source(s) of valuable enough intelligence data, they can keep paying for it, year after year.
Not just in money. They can keep the operation staffed. And they can afford to wait.
As a defender against such adversaries, you will ALWAYS be at a disadvantage. You need to keep a complex, ever evolving system secure and shut attackers out, plus you can not afford to make mistakes. Your adversaries only need you to make one. If not this year, then maybe one after the next. They can sustain their ongoing operations, while you, as a defender in a corporation subject to quarter-to-quarter thinking, have to keep justifying your work (and the ongoing expense) on systems that only show measurable results when they fail in their purpose.
So while my original statement may not be technically true, for all intents and purposes nation-state adversaries do have unlimited budgets. And no amount of expenditure will make you invulnerable.
0: https://en.wikipedia.org/wiki/Mossad