In my department, typically each student has a finite amount allocated for conference travel. After that, you either apply for travel grants, or (commonly) your

In my department, typically each student has a finite amount allocated for conference travel. After that, you either apply for travel grants, or (commonly) your supervisor will probably have access to extra funding, but it's still a finite resource. Nobody would go to a conference if they had to pay their own way because nobody's paid enough to be able to, quite frankly.