We walked from Noble Dame Cathedral at 9.11am and arrived at Saigon Central Post Office about 9.14am. It is a side opposite building between Cathedral and Central Post Office.
There you could buy a lot of miniatures with cheaper price, but you still need to look around.
Over here, the HCMC, those items sells at Ben Thanh market, Binh Tay market, etc are offering sky-high price. You can consider to buy it if you able to ask for discount at least 70%.
My opinion is, if this going to be a practice, long term the sufferer might be those citizens themselves, because many tourists will comment over the internet. Over the time, people will think that those small-stalls will definitely sells you at very high price, each price offered might be rejected by tourist no matter how.
Just now I did mentioned “you still need to look around”, here I have something I should say worth to share.
When you go into the Central Post Office from main entrance, you can turn right which is the money changer there, a souvenir shop sell cloths at genuine price, although it is not buy 1 free 1. Its price average at 80,000 đ per piece. While the left side, another souvenir shop, its price for each cloth is average 300,000 đ, you get one free if you buy one.
We left the place at 10.30am. Hope this help.