Oracles + Market Data

Are there any services (oracles) offering market data in Ethereum?

Things like the price of Gold, etc.

I have googled a bit and notice that most services use a "callback" model, where I request a price with some gas, and the service subsequently calls a method on my smart contract. Is anyone out there taking a "publisher" approach, where they load the data onto the blockchain? Or would that approach be prohibitively expensive?

fyi: I'm not really bothered about SGX, I just want reliable, trusted data.

Submitted December 03, 2018 at 04:45AM }
via reddit