International SIM card
Those are actually fairly stiff rates, compared with data SIMs from local carriers. I've picked some samples below; other carriers in the same country will likely be similar. In any case, 50€ will buy you several months, not one month!
Orange (in Spain) offers 1Gb/mo for 8.95€ with its "Ballena" SIM (http://movil.orange.es/tarifas/tarjeta/ballena/)
Vodafone (Portugal) offers 1Gb/mo for 10.99€ or 2Gb for 14.99€ (http://www.vodafone.pt/main/particulares/internet-movel/tarifarios/internet-no-telemovel.html)
Vodafone (Germany) has 1Gb/mo for 14.99€ (http://www.vodafone.de/privat/callya-prepaid-karte/prepaid-internet-websessions.html)
One other note: If you are a U.S. T-Mobile subscriber on a "Simple Choice" plan, you have unlimited roaming data outside the U.S. in 120 countries. It's generally 3G, not 4G, but it sure simplified our recent travels!