Anyone can get the trial, yes, but from what I remember the sourcecode for Moonshell is hard as heck to figure out (not to mention that all the comments would be in Japanese).
The compiler used for Moonshell 1.7x is the ARM SDT, and it costs about $5000 from what I remember. Moonlight used it to add some ARM assembly optimizations that weren't possible with DevKitARM and GCC, and once the trial ran out he stopped development.
Also, for all those wondering why nobody picked up development of SNES, NES DS, or any of Flubba's or Dwedit's emulators for the GBA, this is the same reason. Recently Dwedit has been making an effort at porting many of them to GCC so anyone can update them, but for several years the only people capable of making updates had halted development on the emulators.