Upvote:0
A similar cheap prepaid SIM in Hungary could be Bluemobile in Lidl stores. You might try Tesco stores for their service or bigger service providers as Vodafone. Buying SIM cards in Hungary need registration of personal data, so a passport or ID must be at hand.
Upvote:2
Get an unlocked phone at home - it will probably be cheaper, but more importantly easier to comparison shop and take your time to get familiar with the phone.
There are many providers of relatively cheap prepaid SIM cards in Germany, which all offer international roaming and due to EU regulations prices for this have become much more reasonable.
However, for more than minimal international data usage in a short time, ALDI Talk is the best provider I know of, since they have a package offering EU-wide data access for 5 EUR, valid for one week and recently upgraded to 120 MB:
http://www.alditalk.de/nord/Surfen/EU_Internet-Paket_120.php
But I'd still heed Vince's comment and get an offline map app, since intensive use of a map app can use up 120MB more quickly than you'd think.