Just look at for how much a room at one of the Ibis hotels goes (150 - 200SGD depending on season / period) and you will get an idea about the HIX. I would expect a 10-20% premium in rates over that due to location (Orchard / Clark Quay) and likley somewhat higher standard. Not a bargain.
Sometimes the HI Atrium has decent rates on weekends during "low demand periods" I heard. A friend scored 144 SGD (net) a few weeks ago Fri - Sun. If you want to pay less than 100SGD all you have to chose from is Hotel 81 or Fragrance