you can use military spending as a proxy.

I don't think you can, I expect different countries to have a wide variety of intelligence budgets as a percentage of military. But, if you did this anyway for the US and China, you would get 3.1x, closer to 2x than 10x.

Also difficult to know if the CIA gets as much spying done per dollar spent.

You could use investment in companies that the CCP has investment in (and generating revenue for them; which also acts as taking revenue/fuel away from competing government types/ecosystems) as a proxy as well.