Helsinki, Tallinn, Riga, Stockholm by ferry and bus is one of the easiest 10-day loops in Europe, and data costs the same in every stop on it.
Our pay-as-you-go price, checked 10 Nov 2026: $1.08/GB in Finland, Estonia, Latvia, Lithuania, Sweden, Norway, Denmark and Iceland.
Rough maths at ~1.2 GB a day (maps, ferry and bus tickets in apps, photos): 10 days = 12 GB, about $13.
The trap is the ferry, not the countries. Out at sea, the big Baltic ferries run their own onboard maritime network, and a phone that roams onto it can be billed at satellite-style rates. Before boarding, switch network selection to manual or turn mobile data off until you see a land network again, and use the ship Wi-Fi for anything heavy.
UK and US visitors: you don't get EU roam-like-at-home here, so check what your home plan charges before relying on it.
Every country, cheapest first:
Disclosure: these are Silent eSIM's own rates. Anyone done the Tallinn day trip from Helsinki on mobile data only?

Silent eSIM
Mobile data price per GB by country | Silent eSIM
Silent eSIM pay-as-you-go data prices per GB for 218 countries. Cheapest is Ukraine at $0.76/GB. Same USD catalogue as the rates page.