Roshi should only be around 210 btw.
I've saved 310 in about 4 months. I could have had about 350. But I don't buy seals at all, the only times I get them are from SWB, Chase missions, Monthly check in, Matsuri, survival trial, Great Ninja War packs and if they happen to be a bonus for other events that I do. Of course you c*so get them from Sealed Ninja, probably the same odds of getting them from Survival trial. If you do everything you can daily then you should be able to save up a decent amount.
It is hard to save at first because you are addicted to doing those 10 draws every time you can but after a few weeks you won't even have an impulse to do draws. Its like quitting smoking. Sometimes it will get hard seeing your friends and often times rivals getting some really cool and powerful ninja, just keep telling yourself that in the end the ninja you are after will make the current teams essentially worthless.