Minato and Obito do show up in other events (In China, they showed up in treasure of the sages). Deciding where is the cheapest is hard to calculate since on our server, we don't have a lot of events in past that have them and occur frequently. I can't seem to find the forum post that I saw the estimates but they both cost around 12k-14k each in fateful choice so you'll get more than half you spend your coupons this week.