Several domain registrars / hosting providers (including Njalla) accept Monero, which is as untraceable as you can be. Or Monero can be used to indirectly pay a bitcoin invoice very easily (even Namecheap accepts bitcoin)
It doesn't matter. You can buy Bitcoin with cash, convert the Bitcoin to Monero and then as soon as you send that Monero to your own wallet, you're done. You have digital cash to spend anonymously.
The way Monero works, you can simply have two monero addresses/IDs. The one you get the initial coins (cash, bank transfer, doesn’t matter), then transfer to the second one. Then you can buy whatever you want anonymously from the second one. That’s the whole point of monero, that it is not possible to trace transfers, to the contrary of bitcoins where every transfer is in the ledger.