You can buy daily BTC/ETH which is delivered at 4pm, and the fee is a flat $5 per coin (so ~0.01% at the current BTC price). BTC is traded in 0.01 increments and ETH in 0.1 increments.
Caveat is that only wire deposits are accepted, so the wire fees plus network fees (if you withdraw your coins) can raise this cost substantially if you only trade small amounts.