Mrs. Gardiner's letter to Lizzy gives more detail on what was spent. (I believe that is in this week's chapters, so it shouldn't be a spoiler... if I am wrong, please delete this comment) Somewhere on Pemberley I remember reading what commissions in the regulars cost (in L&T perhaps?) though it may have cost more due in this case to the time constraint. Wickham's debts were over 1000 and 1000 was settled on Lydia. Has the matter of W's debts in Meryton been addressed yet?

Another thing about Mr. G's letter is him "releasing" Mr. B from coming to London for the wedding. I presume this makes it easier for Mr. Darcy's involvement to be concealed, and Mr. G knows his brother well enough to know he wouldn't stir himself unless absolutely necessary. Even Mr. B's thanks to Mr G. --- whom he thinks has laid out a great deal (and not just in money but time and effort as well) was "expressed concisely." I know Mr. B is embarrassed and angry at Lydia's behavior, but really, I think he behaves poorly here.