don't overdo it and keep your cool as often difference in rates doesn't justify time and possibly transit expense spent. I know somebody who got excited by XOne rate 33.40 for 1$ compared to his local of 33.00 at Ari area. Spent 1 hr. round trip , saved 120 on 300 $ exchange , out of it 70 went for BTS ticket so total saving was indeed enough for Chang and small bottle of water at 7/11