What does SVB charge for an ACH debit?

The cost depends largely on your ACH volume, but is generally less than $0.50.

Thus, ACH is known as a low-cost alternative to credit card fees, which charge a percentage of the amount.

Problem there is that you're exposing the participants to volatility risk. if btc drops in price then people might be less likely to participate. Many view bitcoin as a great new technology but its price is still too unstable to actually quote products/prices/prices in. Quote in dollars, delivery bitcoin and everyone wins

I guess I imagined that being exposed to volatility risk is something that anyone involved in Bitcoin came to terms with a long time ago.

Yes, but the smart ones learned to minimize their exposure.

he probably funded the first 10-100 btc, 20% profit. do the math.

are you sure 20% profit is the right number? Imagine two people use it, and they both pay 1 BTC.

  Time | Event
  1    | First person pays 1 BTC
  2    | Second person pays 1 BTC
  2    | First person gets paid 1.2 BTC

The creator makes .8 BTC in this case. Pretty solid return if you ask me.

Only if you ignore that the 3rd person would get the 0.8 BTC (as long as the scheme goes on). At some point he stops, but how much money he made depends exactly on how many people he didn't pay back. So, in the simplest case:

    Time | Event
    1    | First person pays 1 BTC

The creator makes 1 BTC in this case. Even better return.

Keep going. Then a third person joins. Second gets 1.2. Creator now has only 0.6. Then a fourth one joins…

my thought process is: one large BTC pool. all transactions are feed into the pool. the order of the deposits dictate priority of withdrawal. Owner does not skim the transactions, only makes a large initial deposit and then markets the site like crazy. Big assumption here is that he is running an "honest" ponzi operation.

why would he even need an initial deposit? he can simply delay to pay people until enough other people have paid.

So that he can "honestly" take the 20% additional of that first deposit.