I'd probably pay 0.5 bitcoins but it depends on the response you get obviously since that effects the probability of winning.

bitmarket has had transactions of roughly 60,000 btc in one year. That means an average of roughly 5000btc of transactions a month. Even if you put a standard 1% fee on them that would only net you a return of 50btc a month. That's about $650 a month. Who would invest $270,000 for a return of $650 a month. Yes you could argue that it would be possible to get more users and more transactions but that is an enormous risk, especially since most users may have now lost faith in the site.

I just don't see how it's feasible.

He seems honest but 19,980 bitcoins are missing. That's roughly $270,000 worth. I just don't see how it can survive that.