I was intrigue by that !!! it's a good question and i think i have the answer.
I recently got an agenda pm damier azur on ebay, which price is 190 euros on Lv french website.
The owner sent me the package and guess what !!! he bought it at monaco on 2008 !!! and it's still the same price!!
So even if in Monaco you save tax, LV doesn't adjust the price for them.