Head brewer/owner of the local brewery here in Bendigo (with a background in chemistry) assured us at a homebrewing info session that boiling and/or campden will NOT make any difference to chloramine levels at all. Makes me wonder why so many people constamtly harp on about using it to remove chloramine from tap water.
At the brewery they use an activated charcoal filter, but he said that for a homebrewer, ascorbic acid is certainly the best option. Just buy some off ebay for peanuts, or from your local pharmacy (just make sure to get it unflavoured, and without fillers ie. powder not tablets!).
Dosage depends on the ppm of chloramine in your local water supply. Dosage in grams = ppm of chloramine * 2.5 per 1000L of water (here in Bendigo where we have ~3ppm, I use about 25L of water per batch, so I would use 3*2.5/(1000/25) = 0.1875g of ascorbic acid for 25L of tap water)