Is there any way to hack it so that the free trial never ends? (And, of course, I will pay for it if and when I can afford it.)
The easiest is probably Xcode, since it requires only installing from the Mac App Store or the OS install CD (depending on the version of the OS you have). The Xcode editor isn't amazing, but it is still quite good for coding and if you're just starting it should be more than enough.
Most other editors included with the OS require a terminal; but that only makes them less pretty, not any less powerful. (I'm ignoring TextEdit because it is not a code editor.)
- "nano" is likely to be the simplest to use; it's a GNU emulation of "pico"
- "vim" is WELL worth the effort to learn as it is a truly superb programmers' editor once you learn it; but I'd suggest reading up on it first, as the commands can seem arcane at first until you learn them
- "emacs" is another excellent editor, that I personally don't prefer but it would be as worth learning as "vim"; there are religious camps in favor of both tools, so it may come down to whichever you like more
- there are still other editing tools that I won't mention because they're pretty obscure, but the Unix core has plenty