The order of currency name and its numerical value (i.e. 人民币五十元 vs 五十元人民币) I tried to search for a sample sentence at jukuu to understand the grammartical rule regarding which is ahead of the other, and got the following sentence.

去广州的票价是人民币九十一元。
他的债务共计为人民币五百元。

The order seems to be currency + value.
However, in another sentence I got the following sentence:

一美元价值8.2元人民币。

In this case, it is value + currency.
So now I wonder which is the correct way to express the currency and its numerical value. Is there any rule regarding this? And is it consistent among different currencies and in all magnitudes of units?
In '人民币九十一元',  '人民币' modifies '九十一元'- (91 dollar --> 91 dollars in RMB)

In '九十一元人民币', '九十一元' modifies '人民币'- (RMB --> 91 dollars of RMB)

They mean the same, and you can use either one.

In '一美元价值8.2元人民币。', '一(元)' modifies 美元 (USD --> 1 (dollar) of USD); '8.2元' modifies '人民币' (RMB --> 8.2 dollars of RMB)