Been there and done that years ago. I remember developing film from the first road trip I took back in the day. I had one tank, two reels. I developed film for weeks. Not fun after the first few days. I ended up getting Jobo tanks and now I have two 5 reel (35mm) and one 2 reel as well as extra reels. I also have a couple ss tanks for color and Minox. Having the Jobo tanks makes it enjoyable to develop film these days. They are so quick to use. I kick myself for not buying more when they were cheap.
Aside from biting the bullet and buying some larger tanks, the other option is to borrow some tanks. I see you are in Japan, so I can't help you with that one, but maybe you know a kind soul. Perhaps you could have a friend help you with the developing as well.
A lot of people say time is money, but I prefer to avoid the drudgery. After several days of developing the excitement wears off and it becomes a chore.
Good luck!