Here is how I look at it. The cost for the PS4 and PS3 is the same. Meaning the game (if only purchased for one platform) is the same $60 regardless of wether it is for PS4 or PS3. The catch is that PS4 simply get's half the game share slots (half resells and half phantoms), so the cost of one PS4 slot is equal to the cost of two PS3 slots. If the cost is $70 (game+upgrade), I think that should be split 50% per console, and the $35 per console is then split between the resells/phantoms on each platform as appropriate. The result on a $60 game plus $10 upgrade is:
PS4 resell: 23.33
PS4 phantom: 11.67
PS3 resells: 11.67/ea
PS3 phantoms: 5.83/ea
You may have noticed that I split the $10 between everyone. I don't think it is a cost only to the PS4 owners. Everyone is actually saving from the cross-platform share, and as such everyone should be chipping in for that upgrade fee.
As for DLC, I think the same should apply. If a PS4 owner buys it they would be paying the full price by them-self, while two PS3 resells could split the cost. That should carry over for the cross-buy, where the PS4 resell pays 50%, and each PS3 resell pays 25%.
In other words, if it was purchased at full price for $60+$10+$50, I think the breakdown would be:
PS4 resell: 48.33
PS4 phantom: 11.67
PS3 resells: 24.17/ea
PS3 phantoms: 5.83/ea
(the above pricing does not factor in the discounted price on Amazon nor the $10 credit)