What could be of interest to you is lycamobile.de who give away SIM cards for free and offer a "International Flat" for € 19.90 per month which includes unlimited calls to all Hungarian networks (including mobile networks). SMS are billed separately with € 0.09 per message. Among several other
tariff options they have a 750MB data pack for € 9 per month and a 2GB pack for € 19.90. Please note that after exeeding the data allowance you'll be billed with € 0.19/MB. Lycamobile is a prepaid service and uses the Vodafone network, which offers excellent coverage and data performance.
The other alternative would be Lidl who have different data packs and charge € 0.09/min for calls to Hungarian landlines and € 0.29/min to Hungarian cell networks, while SMS messages to Hungary cost € 0.19. For details on Lidl check out
LIDL mobile - Prepaid Wireless Internet Access and the corresponding threads in this forum.