Depends, take a walk around your neighbourhood and there may be a local glass shop that can cut a sheet to your size. I suppose the furniture stores can do the same, and add their markup on top of that. For a 5' x 3' sheet, should run you ~$300 not including delivery and doesn't have to be very thick.
Off Queens Rd Central, around in front of the Wu Chung House (where the post office is, next to the Hopewell Ctr), there are a few alleys heading north, there are a few shops that do glass and steel work that will do it on the spot.