How much if you don't win?

Stop looking for the next unheard of exchange to go bust, just use kraken or coinbase

Yeah, this way you don't know what the number is until you actually figure out the vulnerability.

Would be nice for this to pick up, it's a lot more in line with the spirit of bitcoin and cryptocurrencies than fully centralized platforms.

For those that want to have an actual go at it: when deploying it with hardhat for example, you can pass in Math.floor(Math.random()*1000) as the constructor argument in the deploy script, and then see if you can derive the number on the first guess.

Nice challenge!