There are more ways to get data roaming at relatively fair price with Hungarian SIM cards also:
1. Buy a T-Mobile prepaid card and top it up. You need to register for a SIM in the huge stores, gas stations etc. (cards bought there will not work without activation) but you can go to smaller GSM shops in Budapest (the ones sell second-hand phones as well) and can ask for an activated prepaid SIM card. Some of the sellers are really nice and surprisingly have some of those activated cards on stock.
Activate roaming:
*104#
After that you can use the Travel and surf option (send the text "+SURFS" or "+SURFM" or +"SURFL" to the 1430 number)
You can use the +36 30 3444 888 number from abroad instead of 1430 also.
For your information: 1€ = appr. 300 HUF
Data roaming plans:
Travel & Surf S: 690 HUF/10MB data in EU (+Norwegia, Iceland, Andorra and Liechtenstein)
Travel & Surf M: 1490 HUF/50MB data in EU (+Norwegia, Iceland, Andorra and Liechtenstein)
Travel & Surf L: 6990HUF/250MB data in EU (+Norwegia, Iceland, Andorra and Liechtenstein)
Travel & Surf works for 100 countries anyway, not only in the EU.
If you want to call T-Mobile Hungary in English:
Call 1777 and press 9 for English
If you want to use data in Hungary read this:
http://www.t-mobile.hu/english/mobilinternet