If you dig this message board you will find a mention of 1000 ETH.
Which is $876K I believe as of today.
Which illustrates the problem with deposits - you want the validators to be executed by independent security professionals, but whats you may end up with is a highly centralized system owned by miners. Miners have lots of money and lots of incentives to control validators as well as lots of technical knowledge to run validators. In the current system, what is pretty much guaranteed to happen is large miners are going to buy up validators and then they control everything.
It may be that one should have a hybrid system, where there is a reasonable deposit (say $10K), but then you need both to deposit money and get enough community stake votes to become a validator. So it is delegated stake + deposits.