WWE network is $10/month and includes all PPVs which used to sell at the same price as UFC PPVs and do better numbers that UFC are putting up today.
WWE network has 1.6 million paid subscribers, Fight Pass numbers are hard to come by by since Zuffa and WME are privately held but I've seen estimates from 100,000 to 450,000. Let's go with 450,000 and say if the UFC added PPVs to Fight Pass they'd add one million buys = $120 million dollars revenue per year - minimal cost of extra bandwith - whatever international buyers like BT Sport in the UK pay.
How much does UFC make from PPV sales?
According to
http://mmapayout.com/blue-book/pay-per-view/ the UFC sold 8,775,000 PPVs in 2016. WMG make ~$30 PPV per PPV which is $263,250,000. However that includes 2 McGregor fights, one Rousey fight & UFC 200 so better that you'd project for, say, 2018. So for this year the UFC has held 5 PPVs and sold 1,050,000 PPVs + whatever they get for Aldo-Holloway. They'll end up selling half or slightly less than half of the number of PPVs they sold last year, which would make the maths very close - assuming they add 1 million subscribers.