Thanks a bunch everyone, this has been really helpful. Based on your advice, I'm thinking that getting a morph first might be a good idea, since as far as I know the only extra cost for a morph is the price of the snake itself, and if I know I can afford the running costs of a BP (which I promise I will check very carefully, I don't want a pet if I can't do a good job with it) I'm perfectly happy to save up for a while to get the snake I really want.

The other benefit is that I'd definitely feel most comfortable getting a first snake from a breeder, especially since I have very limited practical experience with pets so it would be good to know that a) the snake I get is in the best shape possible and b) I have a source of really good information about it. If I want to get normals later, I can then get them from a shelter or rescue. Because I do agree with the idea that you should, if possible, get a pet from a rescue, but finding a morph in a shelter is going to be much more difficult than finding a pretty normal (as most normals are very pretty).