I got him for 30 seal scrolls, some in my server got him for 60 seals so it depends but most likely not more than 210 seals.

It depends on ur luck. I got him with only 10 or 20 seals I guess cuz I always open treasures using 10, 20 or 30 seals n get my rares from just spend not more than that. I rarely use more than that cuz I thought i'm just gonna waste those seals if I got nothing worth with them.

It's one of the common rares in the treasure, i got mine at 70 but this doesn't mean anything. Every 6-7 draw by ten in the treasure you get or him or bee samehada (yugito nii is not considered a common rare but a simple common even if is in the destined ninja list). So it's up on your luck. Could be you are unlucky and before getting roshi you get bee 3 times, but is very unlikely.

So we get bee after yagura mostly ?

I got mine at 130, Bee at 70, another Bee at 200, and Roshi at 210...though

You only needed Yagura, right? He tends to be after Bee most of the time, but as seen here, he can be obtained pre-Samehada Bee

Thnx