You can hunt down the ITV Spots cost ppt online.
I am utterly ignorant of how much this kind of venture costs the RFL
But as a guide a 30 second advertising slot during Corrie costs;
Yorkshire - £4400
Granada - £5470
London - £11490
Slots vary massively in cost of the course of a day for example on Granada at 11am you get a 30 second slot for £620, presumably one man and his dog watches in border at this time as that's only 50 quid! To go nationwide costs between £6,200 for the 11am slots up to £60,390 for the 9.30pm slot, which soon adds up if you air a few times!
Of course on top of that you've got production costs, any other fees and negotiations around the +1 channel to take into consideration.
Great initiative, can see the sense of just going Granada and Yorkshire for reasons already stated by others.