For clerkship interviews, you must make the necessary travel arrangements at your own expense. Therefore, consider geographic distance before applying, not after you are called for an interview. It is not acceptable to turn down an interview because you cannot afford to travel to the judge's chambers.
If you are invited for an interview in a distant location, call the other judges to whom you have applied in the same area and try to arrange an interview while you are there. Many judges are quite amenable to accommodating your travel schedule. Taking this leveraging step not only will save you time and money, but also might create interview opportunities that you would not get otherwise.
Finally, students on financial aid should check with the Financial Aid Office about the availability of short-term and emergency loans, which may be available to help you to spread out the expense of clerkship interviewing.