It's a lot more than that. It's getting a license to release the Quad mix and possibly getting a new license to reissue the stereo mix if the license is already expired. Plus, there's the new mastering costs for the Quad mixes and the manufacturing costs for pressing the SACD again but this time with the additional mix.
AND it may not sell as well the 2nd time around if the stereo SACD crowd already has their SACD of this title and doesn't feel the need to buy another one.
All in all, I think Audio Fidelity are wise to release other titles in the meantime until there becomes more of a demand to reissue BDB yet again on SACD. Plus there will always be some who would prefer they reissue the 5.1 mix on the SACD instead of the Quad mix anyway.