I got the student (freeware) version of C18. I guess after 90 days, some of the special features become unavailable, but it should still work fine for "garage/basement Engineers"
Yeah I think after the 90 days you're restricted in terms of code optimisations. This may or may not be a problem, depending on your application.
The problem is that if you're hoping to do a homebrew project and then sell it as a kit (or as a completed unit), you're not strictly allowed to do that using the free version of Microchip's compiler. In order to be legally allowed to do that, you have to purchase a version with commercial permissions - which is where the thousands of pounds comes into it. For the garage/basement Engineer who's doing it mainly for the fun of it and hoping to maybe sell a few projects here and there along the way, it doesn't make sense to spend that sort of money on a compiler. There are plenty of other things you could spend that on first!
That's where Sourceboost's compilers come in to play. I purchased a fully licenced version of their compiler (with commercial permissions) for just over £100 I think. Very reasonable, and within the reach of hobbyists. If you don't care about commercial permissions but still want the optimisations, you can get an even cheaper version.
Of course, the fact that you're not strictly allowed to use Microchip's free version of the compiler for commercial purposes doesn't necessarily stop you. It's not strictly legal, but if all you're doing is selling a couple of homebrew projects here and there... well you're not likely to be hunted down and caught really are you. On the other hand, if you're a big company selling professional products using their compiler, then that's where you really need to be buying the commercial licence.
Anyway, the op has stated that he doesn't care for commercial permissions so I guess the point is moot. But it is something worth considering if you're planning to marry yourself to a specific compiler and you want commercial permissions in the long run.
Having experienced both Microchip's compilers and Sourceboost's compilers, then I would say that Microchip's compilers are much more friendly to work with. So if you're happy to use the cripplied version of Microchip's compiler than you're probably better off sticking with it because it's definitely a better product.
On the other hand, if you want your code to be efficient, or you want a commercial licence, but you're only a hobbyist, Sourceboost is for you.
Brian