[Alneyan]

In the case of Soul Contracts, a mod could also be used to alter the effect of the item, if you think such a change is needed. As I do not think we can currently mod magic items (I haven't checked under 2.13 though), the solution would imply a weakening of the Devils themselves, and a change of the cost of the "Bind Devil" spell.

The Soul Contract will still be a long term investment, but it would then take longer to pay back, while making direct summons cheaper as well. The actual changes are left to you, depending on your mileage. Sure, a mod will unlikely be widely used, but it should do just as well as a house rule in this case. And if magic items can currently be modded, it would be much easier to do something along these lines (the same reasoning would go with clams and the like, but it would be harder to do it with an indirect change).