Back of a envelope calculations.
BT paid £152m for 4 seasons, so a 30% increase on that would be about £200m for 4 seasons.
From what I can see, something like 350k were watching each weekend, so best case scenario is all of them would be interested in a service (some wouldn't, others would come in with it depending on cost).
You'd basically be looking at about £12 a month. Maybe less though, since clearly there's advertising opportunities to sell at half time, pre-match etc.