Accommodation in central Birmingham is relatively expensive.  But if you are prepared to make a little effort there are rooms available in less desirable locations or establishments at a very reasonable cost.

Birmingham does have a good suburban rail network (and buses?) so you don't have to be in the city centre.

Travelodge at Perry Barr has rooms at £32.  It is a mile from Perry Barr Station, which is a 14 minute journey from New Street with trains every half hour in the day.  This is right by Junction 7 of the M6.  This hotel is on the same side of the centre as the conference venue and is described as 3.3 miles from Birmingham centre. No Tripadvisor rating so maybe it is new.

On the other side of Birmingham are the Travelodge at Birmingham Oldbury - that's a couple of miles from the nearest sation so less convenient - and the excitingly named Travleodge at "Frankley M5 Southbound".  Both these offering rooms under £30 at the time of writing.  Tripadvisor rated the M5 hotel 93 out of 137 Brum hotels.  My experiences with Travelodge have been positive but obviously not true for everyone. The Oldbury one gets rated 2 out of 3 Oldbury hotels which is not a lot of use - individual reviews are either very negative or pretty positive. 

Other places that came up in searches are nitenite, offering rooms at £59 - much more central and getting good reviews on Tripadvisor.  Etap is the only other half-reasonably priced central location at £55:  1 Great Colmore Street, B15 2AP.  Rated 67 out of 137 hotels on Tripadvisor.  Under 1km from the cityr centre though the wrong side of New Street for the Conference Centre.  

If you are staying over in Birmingham for the Conference, why not add a comment to say where, so maybe some of us  can meet up?