What are the roaming charges in Spain?

It depends. Spain is in the EU, so "Roam Like at Home" applies only to EU citizens.

• If you are from the UK (Post-Brexit): Most UK carriers (like O2, Vodafone, Three) have reintroduced daily roaming fees (e.g., £2-£6 per day).
• If you are from the USA/Canada/Asia: Your home carrier will charge expensive international rates (e.g., $10-$14 per day).

A esimFlyer eSIM is a one-time prepaid fee that is significantly cheaper than these roaming charges.