A friend has stayed at the Robertson Quay and recommends it. Up the river in the river district.
Last trip I considered the Hotel Asia, a long block off Orchard Road but walkable. My local contacts told me it was an OK place to consider.
For top location, affordable, next to a subway stop, all my trusted guidebooks recommend the Albert Court Hotel near downtown. Three stars for $58 USD on Expedia looks quite a deal. The one time I considered booking it, it was full while there was still availability nearby, and I figure the best deals fill up first.
Do note that prices in SIN have a + and ++ and +++ etc. after the price. That stands for the This Tax and That Tax that get added. Adds an easy 20% to your bill.
Enjoy visiting a safe clean city. Just remember, no chewing gum and no jaywalking.