If you wish to stay longer than 90 days you typically have two options:
The fee is currently 180 euros (there are some exceptions that might make this fee lower), and you must provide evidence of sufficient funds and have private health insurance for you and your dependents in order to apply.
To qualify, you need to prove that you have enough funds and private health insurance. You’ll need to prove that you earn 2,000 euros a month plus 20% for your spouse and 15% per child. Funds can be through your pension, bank balance, or other financial resources. Alternatively, you can show that a deposit of 24,000 euros has been made into a Greek bank account in your name.
If you’re interested in making a bigger commitment to the country, then the Greek Golden Visa might be an attractive third option for staying long term.