If you apply to schools on both coasts and in between, you might have to buy a lot of plane tickets. Besides the options mentioned by @Aaaaaa2 , be aware that some schools have a program where current med students host you overnight at no charge. If you apply regionally, you may be able to drive to interviews and not need a place to stay overnight.
I'd say roughly two days per interview - fly in the day before, fly out the day of. If they're clustered together in a same area (ie. NYC), you can save your travel cost.