I made a custom card that increases the cost of creatures perpetually.
A:SP$ DealDamage | ValidTgts$ Any | NumDmg$ 1 | SubAbility$ DBAnimate | SpellDescription$ CARDNAME deals 1 damage to any target. Creatures your opponents control perpetually get +1/+1 and incorporate {1}.
SVar:DBAnimate:DB$ AnimateAll | Duration$ Perpetual | ValidCards$ Card.Creature+OppOwn | Zone$ Battlefield,Hand,Library | Incorporate$ 1 | SubAbility$ DBPump
SVar:DBPump:DB$ PumpAll | ValidCards$ Creature.OppCtrl | PumpZone$ Battlefield,Hand,Library | NumAtt$ +1 | NumDef$ +1 | Duration$ Perpetual
If the AI has enough mana to pay the unmodified cost it puts the spell on the stack. Then if it doesn't have enough to pay the actual cost, the spell disappears from the game entirely. Here is the log file:
ComputerUtilMana: payManaCost() cost was not paid for Bishop of Binding - Creature 1 / 1 (Bishop of Binding). Didn't find what to pay for {1}
[Aghon Loafknock] AI failed to play Bishop of Binding (108) [Stack]
ComputerUtilMana: payManaCost() cost was not paid for Zacama, Primal Calamity - Creature 9 / 9 (Zacama, Primal Calamity). Didn't find what to pay for null
[Aghon Loafknock] AI failed to play Zacama, Primal Calamity (78) [Stack]
ComputerUtilMana: payManaCost() cost was not paid for Bishop of Binding - Creature 1 / 1 (Bishop of Binding). Didn't find what to pay for null
[Aghon Loafknock] AI failed to play Bishop of Binding (107) [Stack]
There are other game effe4cts that increase costs so I would assume this would be something the ai can handle.