I think you buy the equipment yourself and scape you tank urself and let them do the monthly cleaning or can also clean the tank your self is much much cheaper.
I think to set up this size tank will cost you about $4k to $5k only
And it is my first time keeping octopus.
I learnt my lesson when I have too fine sand as the octopus keep messing up the sand, but now I don't use the fine sand anymore
For me just put the bag in the tank for half an hour and put the fish in the tank.
I did that also to my octopus I bought from irwana last week and it is very stable now.