Registry fees alone will cost you a minimum of $100k a year even if you sell no domains. You also need to submit business plans and "proof" of economic viability; without those your application will be rejected. One factor that most people aren't aware of is that ICANN will require you to have enough money in reserve to keep the registry alive until a new buyer can be found in case things go bad; this can be as much as $4 per domain sold in cash as reserves. If you predict you'll sell 4 million domains you'd better account for the fact you'll need to keep $16M in the bank.