This is certainly manageable to do, if you do apply early and apply very broadly, regardless of how competitive you are. It will also depend on where you are based during the application season. For example, being based in the UK will be much more reasonable than being based in say, South Korea.
I applied from abroad this year while getting a master's degree in the UK (still ongoing). In total, I ended up making 3 additional trips other than winter break (did 2 interviews then) for flying back to the States (two in November and one in February). I was fortunate to get into my top choice school in late November, so I was able to turn down 2 interviews that I was offered later in the season. Ticket prices for me were actually quite reasonable and comparable with domestic flights, even for last minute fares, since I was using miles with AA and my parents are small-business owners who have AA frequent flier cards. I also had elite status with AA, which really helped with getting on standby flights, choice seating, etc. Booking tickets on miles is also great for switching dates and the flights themselves after you initially book, as long as you're keeping the same origin and destination. This is really good if you end up getting another interview and want to schedule it near another trip you're planning back to the US.
If you do plan to study abroad while applying, I have a few other pieces of advice not mentioned so far:
1.) Try and base yourself in a location with nonstop flights to a number of US destinations, ideally with one carrier. Having a direct flight to your interviews is so much less stressful and physically taxing. Of course, you can't always control for this with the schools you choose to apply to, but try your best to make this happen. If you can bunch your interviews, save the schools in obscure locations (Providence, RI; Milwaukee, WI; Burlington, VT etc.) for when you're already traveling around in the States.
2.) Invest in comfort. Medical school interviews are a big deal and it is absolutely worth paying more for a few luxuries if you think they help you stay rested and perform better in your interview. This would include small things, like getting a neck pillow for a west-bound international flight, but also opting for an Uber/taxi instead of navigating a new public transit system with overhead baggage, staying in a hotel, and investing in Global Entry to avoid long lines at immigration. This will save you time and effort, which I'm sure you'll appreciate after an international flight. You have plenty of other occasions to save money.
3.) Use miles whenever possible, and if it's cheaper than booking with money.
ThePointsGuy has a calculated conversion for points to miles, based on the credit card and carrier that you're using. If you don't end up having enough frequent flier miles to pay for international flight tickets, look into using a travel agent. Paying for tickets means that you're stuck with the dates that you initially book though, so this isn't a good idea if you're booking flights in September for an interview date in November. A lot can happen in between that time.
4.) Consider the effect of jetlag based on time zones and the direction that you're traveling. For example, there is a 5-hour difference between the UK and the East Coast, so it actually made sense for me to stick with UK time when I was visiting the States for interviews for a short amount of time. It takes about 1 day per time zone to adjust for jetlag. You should keep this in mind when traveling.
5.) Set up a Google Voice account in the US before leaving for abroad. This will allow you to make calls to cell phones and landlines for free, via Google Hangouts on your phone or your computer, for not only keeping in touch with friends/family, but also for calling admissions offices and coordinating logistics from abroad. Phone calls are much more effective than emails with scattered responses spread across time zones.
To be honest, I actually had a great time applying from abroad. It was an interesting challenge, it was a nice ice-breaker with other applicants on my interview days, and interviews and admissions staffs seem to really appreciate the effort that I was making to come visit their school. It really goes a long way in demonstrating interest to the school, and it added pressure for me personally to go out and collect as much information about each school as I could, since I was already traveling 7+ hours to make the visit. The plane ride over was also a good time for me to collect my thoughts about what I wanted to communicate to the school during my interview, and to gather some intel on each school before visiting.
I hope this helps! PM me if you have any other concerns or questions.
