Well according to the Budget published in the Official Journal ofthe European Union dated March 8th 2005it cost:
Budget Line 372
Contribution to the Fund for the financing of the Convention on the future of the European Union
Chapter 37 Total
Euro 38 239 968 in 2003
Euro 43 574 000 in 2004
Euro 55 078 500 in 2005
Even with my bad maths that adds up to a grand total of...
Worth every groat I am sure.