604 numbers are readily available from Public Mobile in smaller communities around the Lower Mainland like Sechelt (local call from Vancouver), Squamish, Powell River and Hope (long distance call from Vancouver).
Typically the cheapest option is to buy a SIM card when you arrive at your destination. Every country is different so research the options before you leave:https://prepaid-data-sim-card.fandom.com/wiki/Category:Europe If you're going to the UK, Giff...
A local SIM card purchased when you arrive at your destination is usually the best value. Check the Prepaid Data SIM Wiki for country-specific information about local prepaid options around the world.