The money changers in Raffles Arcade (some of them) can cut checks, too. And typically not for what Citibank charges.
I was aware of all that when I posted that advice.
So there we go: a cash option (in SGD, obtained at Raffles Arcade for example) and a (lower cost than Citibank) first party check ("international draft") option (in USD or any other major currency, same place). Note that the cash option is likely to be lower total cost for USD50, even with the double conversion (USD to SGD at Raffles Arcade, SGD to USD, apparently, at the broker). The drafts do cost some money for the money changers to cut, and they pass on that cost.
Maybe the original poster could explain, precisely, what he's trying to do. What is he trying to accomplish in that brokerage account? Start with that. But getting (legal) funds into a brokerage account is not hard. SGD cash, first party check, and first party wire all work with this brokerage. USD cash is convertible to SGD cash at Raffles Arcade (and elsewhere), and brokerages know how to convert SGD back to USD if that's what's required within the account. If the original poster is requesting that somebody write him a check in Singapore, that'll be a (third party) SGD check. But why would a SGD help (except for money laundering a small amount of money)? The broker might not even accept a third party check. The broker is already willing to take SGD cash (in reasonable quantities, presumably), so go with that! Or go with a first party USD check (called an "international draft") obtained from one of the Raffles Arcade money changers that offers that service, an instrument that no individual here in this forum can provide.