In addition to mental and physical demands, McGregor (19-3) estimates he's spent $300,000 during preparations for the fight.
The Irish star suffered the first loss of his UFC career in March, submitting to a rear-naked choke from Diaz in the second round. Rather than return to defend his featherweight title, which he still holds, McGregor demanded an immediate rematch against Diaz.
Preparations have taken place in Dublin, Iceland and Las Vegas. The 27-year-old has been relatively isolated in the desert since early July. Doing so, with a full camp, has not been cheap.
"With gyms, cars, transport, flights, accommodations -- I'd estimate we're talking a $300,000 camp here," McGregor told ESPN.
"This is a big, big expense -- but what I make is big. So, in the bigger picture, it's rather small."
McGregor's reported purse to the Nevada State Athletic Commission for UFC 196 was $1 million, although he makes much more in undisclosed pay-per-view bonuses.
In addition to head coach John Kavanagh and coach Owen Roddy, McGregor has employed a masseuse, a performance coach, a movement coach, a nutritionist and various sparring partners for this recent camp.
Grappling partner Dillon Danis, from New York, was flown to Dublin, then Las Vegas. Irish middleweight boxer Conor Wallace was brought in to mimic Diaz' striking style. A videographer is also part of the camp, to publish promotional videos for McGregor on a regular basis.
The camp is based out of a six-bedroom mansion that sits on a two-acre lot. It was last sold for $2.5 million.
"This is most certainly not another fight," McGregor said. "I have done things differently this fight. We have been going to war every single day in the gym in preparation for this. So, this is a war to me."
Previously, McGregor has not trained so opponent specific -- mostly because his opponent often changes right before a fight.
In eight UFC appearances, four of McGregor's originally scheduled opponents have pulled out due to injury. Two of the four, featherweight Jose Aldo at UFC 189 and lightweight Rafael dos Anjos at UFC 196, pulled out ahead of championship fights.
But McGregor said he never worried about Diaz (19-10) pulling out -- so, he didn't mind investing heavily in a camp tailored to him.
"I do not recall him pulling out of a contest before," McGregor said. "I'm just able to tell things sometimes. So, I feel he will be there and that's it.
"I'm very happy with that. It's a nice feeling for a change. I've never had that. They always pull. They always have. It's nice to have this feeling that the man will show up. The man I'm set to face will be there. So, the preparation has been there."