You might want to check out Ed Moorman's thread in the glow engines forum about the JBA .56 available from www.kangkeusa.com for $79.99. With a stock exhaust setup, it's liking buying a .55 AX for almost half off:

http://www.rcuniverse.com/forum/m_6762745/tm.htm

I own the Magnum XLS .52A, and I haven't found it any more challenging to tune than my O.S. 2-strokes. There are a lot of good choices out there for powerful, inexpensive 2-strokes.