If I use a credit card(visa, amex) in an ATM machine, the money is treated like a cash advance. All charges on the card then become subject to the CC company interest for that month. This can be very expensive. Withdraw $200, and get hit with 1.5% charge on the $15000 you have racked up for the month!!! I rack up those kinds of charges, and pay them on time. no interest, lots of miles. Cash withdrawals do not buy miles.

Get a separate debit card from your bank that you never put charges on. Find the max chargable. You can also get these cards from Fidelity, or Etrade. Some have very short daily maxes. My bank has a $250 per day limit.

The rates for these cards will vary, but they are the cheapest way to get small money.

for large money, you will have to find a money trader.