IIRC, once you've proven that you can reliably run a registry (which Google does anyway for their other TLDs), the application and fees for an additional TLD is much cheaper than you would expect (5-low 6 figures/year)
I think I remember hearing at DNW that the uncontested TLD application fee and annual fee are flat $185K and $25K. Donuts probably owns many more TLDs than Google, but I'm pretty sure they still paid the $185K fee.
