yeah, coffers rarely go on sale, especially the napa leather ones. the tan/camello/black colors are pretty much timeless and miumiu knows it. when i bought mine, the SA at the miumiu store told me that those colors in the napa won't ever go on sale - but the different variations that may come each season (suede, patent, colored leather, canvas, etc) might once that "collection" is done.
before trying the flagship, i went to Saks to get the coffer through their pre-season sale, but every other bag in the collection was on sale EXCEPT for the leather coffers. blah!