I've 5 M bags.
3 were bought as presents but the others i bought duty free at Heathrow.
I did keep an eye on the sales but the reductions always seemed to be (unsurprisingly) on the far more seasonal colours/styles rather than the classic bags.
So getting a Bayswater in bright green (or other on trend colour) in the sales - easy. Getting black, tan, brown, navy etc - rare as hens teeth with any significant reduction.
However in duty free there was a fantastic range and better pricing than most of the sales.
Btw I have the brown Bayswater - it was my first one. It's 10 years old now and still looks fab, despite being used a lot (ie.not just an occasion bag). It was my work handbag for years and stuffed with laptops, notepads - you name it.
The brass work is no longer pristine but I could have that replaced if I cared (I don't). The leather/stitching etc is all still first class :-)
Out of all the bags it's been the most versatile and if I could only have one it would be that.