As previous speakers have already written. Seek legal advice. Be very open in communication with the BU. That you cannot afford such price increases. Has the BU already named concrete amounts or where do the 30% come from?
Alternatively: There are now some large GUs who pay their clients compensation to get out of the contract because fulfilling the contract (with price guarantee) would become unprofitable.
Maybe, to strengthen your own position, you can also offer that. So take the stance that you do have a price guarantee, but would be willing to release the contractor from the contract against compensation. Then take the 20-30k, invest it well, and wait until things stabilize (I don’t believe it will go down drastically, but currently there would be the incalculable risk of having to accept further price increases...).