for ur budget, i can recommend Excelsior Hotel, its claimed to be four stars. their prices start from SGD160.
Concorde Hotel Singapore,four star. prices starts from 162..
Fort Canning Lodge, 3 star, starts from 142
and this one is a special one, its a boutique hotel. kinda funky. Hotel 1929, prices from 160.
Hotel 1929 only if you don't mind squeezing. The $160 is for superior double, and most of the superior double rooms there are tiny. Husband + wife possible. + kid somemore... maybe best to see the actual room before you book. On the other hand, they got really nice designer chairs there.
An acquaintance of mine from KL said he enjoyed his stay at the New 7th Storey Hotel (which actually has nine floors). It's is a fairly centrally located old hotel (the last hotel in Singapore to have a manually-operated lift that they claim has never broken down) with lots of interesting history & good views of the surrounding locality.
Dont ever stay at hotel 81 chain hotels. They are pay per hour hotels that cater to ladies of the night or people going for one night stands. Unless you want to hear the groans and moans of your neighbours, dont ever stay there.