Ah yes and sometimes you can drive from one interview to another and it's cheaper even if a rental car or hotel in between. Some students have a block off for interviews and do that for quite a few if you daisy chain them. Example: flew to Pittsburg, interviewed, drove 3 hours to Philly, stayed at hotel and interviewed next day. Had an interview on a Friday, stayed cheap hotel over weekend, flew Sunday to next city for Monday interview.
Also going from shorter flights or from a certain hub to another or between certain cities can save on airfare.
Also keep any receipts for interview costs after Jan, because you start earning money in residency in June, you will file taxes for the year despite being a student for the first half of year, and you can deduct some of those expenses to lower your taxes. Look into how your student loans and relocation costs play into that too, and books/equipment you may buy specifically for residency, if you're so inclined. The IRS also has a website to use your expcted resident salary, loans, expenses, to calculate your estimated tax burden which can mean you change your claimed numbers of expenses beyond what the standard forms would suggest. This can increase monthly take home but will decrease your return, careful you don't underpay and then owe tax, but the website can help you plan your budget. (Segue from travel expenses to taxes, but while you're booking your interviews might as well consider the bigger pic.)