More cost effective - a Greece SIM card or Consumer Cellular International Roaming?

Can your phone take an e-sim?

There are plans for 14 days that cost less than $30.00. I have used a European eSIM or physical SIM on 8 trips without any problem in my iPhone. Usually use around 5-6 GB of data on it per trip along with WiFi in the hotels. Vendors in the Athens airport charge an extra €12.50 for a plan. If your iPhone utilizes an eSIM order one ahead of time to save standing in line at the airport. There is a web site (Traveltomtom) that has recommendations for Greece.
Also if you do not have a VPN app for your phone recommend using one when you connect to any WiFi.

Ditto the E-Sim. We use Holafly.

I always get a Cosmote SIM card when I arrive in Greece.

Available at Germanos Stores or even from street sellers in Athens.

There is a Vodophone kiosk at the airport but doesn't sell Cosmote SIM cards but I hear it works well also.

Inexpensive and works well all over Greece including rural areas.

I used consumer cellular international coverage for my recent 26 days in Italy. I use my phone continually for google maps, reading history of places I’m touring during the day, texting my husband and others etc. I never did make any phone calls. My bill came to roughly $17. I’m definitely doing it again in Oct when I go to France.

After Lyndash's reply I opted for CC AND the reason my phone would not be covered under warranty is that until I own it, it is locked and wouldn't accept a SIM card. That would have been interesting since CC activates the phone before it leaves the US. Would have been a great way to start a vacation with my wife's flip phone.