I imagine that they would probably (I don't know for certain) limit the license of a trial version as that would lead to endless amounts of loopholes on the rare occasion that they do decide to go to court over piracy or anything related.
I'm not saying that you should use a cracked copy but what you could do is get one based on the premise that by doing so it would earn you enough money to go and buy a licensed copy, which you wouldn't be able to do otherwise without getting a small loan or something. (High risk much?)
I don't personally believe it's fair to expect students or new freelancers to be able to just throw £600 at a new piece of software in a market that is so incredibly monopolised that there isn't really any other professional alternative. (Yeah, you're gonna walk into that interview with GIMP on your CV?) Yes, you could use one of the free alternatives but who really wants to waste time learning multiple software packages that do exactly the same thing.
It's probably not a conversation best suited for here, however, I believe there are certainly two sides to the argument. But as Levi says, if it's only small scale, simple website graphics that you're going to be doing then it probably would be best to stick with free software.