This is the purpose of the contract. You have to spend $200B, so you go to several large customers and sign contracts contingent on your ability to supply which will guarantee you $300B in future revenue. Now you can raise funding against the guaranteed revenue and the dumping can't change that because the contracts are already signed.

To prevent this the incumbents could go in and undercut you before you actually build anything, but that's not much of a cartel anymore then. Anyone could "compete with them" just by threatening to raise funding.