Accommodation is getting pretty scarce in Canberra for LCA. <snip> So if you haven't secured your accommodation yet, it probably is a good idea to do so especially if you are planning on attending all of LCA from Mon 18 Apr to Sat 23 Apr.
I suggest checking Rydges Lakeside, which has rooms on special for $95 per night for two people (in twin beds) during the week of LCA. They also have the advantage of cable internet in the rooms, though that costs extra, and possibly wireless as well (can't remember about that one).
In the reservations section on their website, look for the "Short breaks (min. 2 nights)" special rate.