In the area around the site of the conference (The King's Buildings - click link for a map of the area), there are a number of good, affordable Bed & Breakfasts (B&Bs).
Some good resources for finding accommodation in Edinburgh are
Rooms are available in Pollock Halls, the
university student accommodation, within 20 minute walking distance
from the conference. More information and online booking at Pollock Halls can be found at Edinburgh First.
Another option is to have a look through Edinburgh.org's Accommodation Site. Here, you will find a list of hotels, B&Bs, and hostels in Edinburgh.