That looks like it would be an AWESOME holiday. I bet the weather there is nice in April.
I second that! I first visited Hungary in 1979, and several times again between 1998 and 2007. If you're looking for a European aikido vacation, this is an excellent choice. Budapest is beautiful, inexpensive, and tourist-friendly. April is very pleasant, especially if you like cool spring weather.
If you go, try to stay on the Buda side, rather than in Pest. The public transportation is easy, but avoid taking a cab unless a trustworthy Hungarian arranges it for you. Do yourself a favor and add some time to enjoy the city and surrounding countryside.
My experiences with Hungarian aikidoka of all organizations were uniformly positive. They are dedicated and attentive practitioners. And they remember that it was not so long ago that martial arts training was strictly regulated by the state, so they have a deep appreciation for the opportunity to study.