Usually when he's in time-limited event (the one we currently have or the on with keys) u can get 4-5 frags for free each time. If he happens to be in mision mobilization, thats 9-10 free frags. It's hard to estimate, but he's pretty often here, so if you keep coupons for the time he's in mission mobilization/lucky board (to get some power as well) and get free frags everytime, i'd say it's 4, max 5 months. Once you get like haf of his frags, you should be able to afford the other half in an event. Same applies to other event ninjas (except hokages, which hardly ever are included in free events), if you want to camp for someone specific, check event threads to see if they appear often.

As for hidan - yes. But that depends on a ninja and on an event- sometimes you can get for free 30frags of someone (last week sailor sakura during mission dealer), sometimes 1 (this week 9tails naruto during time limited). Pretty much each ninja has its own cost and availability which transit in different ammount of time required to get them. If you have someone particular in mind, maybe we can help estimate cost and/or time needed.

^ I've never said that you can get 30 dpb hidan frags, you seem to miss the whole point of the post.