Hi all a few question:
1) is there a cheapest way to fund OX and IB account ?
2) what is the recommended ways to do a withdrawl from OX and IB?
3) isit possible to transfer a funds from OX to IB?
Can't help you with #3, but I can answer #1 and #2 for Interactive Brokers, at least.
Since IB can't handle deposits and withdrawals in SGD, funding and withdrawing is always going to be a bit expensive. The absolute cheapest way to fund it is to set up an American bank account and use ACH transfers from that to fund your IB account (if you've got DBS Treasures, you can wire from your SG account to a first-party US account basically for free, and do an ACH from there); but the more practical way is just to do wire transfers from your bank account. Bring lubricant.
The best way to do a withdrawal from IB is, as Chopra mentioned, international wire transfer.
Until IB starts offering deposits and withdrawals in SGD, this is unfortunately the only realistic way of doing it.