Campy uses a slightly different square taper (ISO) than Shimano and most other cranks (JIS). An ISO crank will not slide all the way up a JIS taper and will not be in the proper position or secure enough. You are right that the proper bb is expensive. Licktons in Chicago want $125 for it.
http://www.lickbike.com/productpage....B='0204-13'
Lickton's also has a 111 mm Centaur square taper bb for much less ($80) and the taper will be correct but I don't know if it will produce the correct chainline.
http://www.lickbike.com/productpage....B='0205-13'
You might try calling them and see if they know.