My friend planned an over night stay in Leeds and 36 people were up for it when she suggested it and then when it came to booking, only herself and her 2 bridesmaids were up for it!!
We ended up doing a night local (we live in birmingham anyway) and just the people close to her (bridesmaids and her sister) stayed over, other people just came for the meal and drinks then went home.
Worked out well in the end as people did what they could afford.
Its so annoying when people say they want to do something and then drop out!!
p.s you have got a really good price for b'ham..... it can be expensive!!