Probably wouldn't even need 5 Million. According the the PBS article about the 2 US Navy sailors arrested for spying around august of last year one of them was apparently only bribed $10k-15K for the year [1]. I was pretty shocked at first but it made sense that with the financial stress many face in today's market a 10K bribe would go along way and have a high return on investment especially if the potential payoff for a backdoor or zero-day is in the millions [2]
>2 US Navy sailors arrested for spying around august of last year one of them was apparently only bribed $10k-15K for the year
This is exactly why investigations for security clearances focus mostly on a person's financial situation: someone who has a lot of debt and shows a pattern of poor financial management, i.e. someone who'd jump at a chance to make an extra measly $10k, is the kind of person they want to avoid giving a high security clearance to, because of incidents exactly like this.
It's a common misconception that clearance holders who sell secrets make a lot of money doing so, and this just isn't the case: it's comparatively small amounts like this. For someone who's deep in debt and desperate, it doesn't take much to buy them.
After Abscam in the late 1970s/early 1980s, one of the quote going expressed surprise not that politicians could be bought, but that they were so cheap.
[1] https://www.pbs.org/newshour/politics/2-u-s-navy-sailors-arr...
[2] https://en.wikipedia.org/wiki/Market_for_zero-day_exploits