Level 5 is master
Level 6 is grandmaster
Level 4 elite would be expensive
Level 5 master would be very very expensive
Level 6 grandmaster will be out of league expensive also not allowed on this forum as there Are plenty of inferno challenges and forum rules state We cant do inferno as a service.
But to get you level 5 master tier.
Its pretty much impossible to calculated a price on this.
Easy/medium/Hard should be possible to price out fairy easy
But elite and master Are very difficult as some tasks Are do 25 cox raids, (1 raid would Normaly cost something along 10m, so 25 would be 250m ish) and thats only 1 task
Full master tier might cost 5b mabye Even more. Some of the tasks are very limited Who Are good enough players to complete them.
So if you would want master tier level 5, then you need to throw in an insane amount of gold.
I would suggest you look into level 3 or 4 instead. But Lmk What sort of budget you have etc