In olden times money used was not like modern money. It was in metal coins - silver, gold Kaansaa etc.

80 Varaat (shells) = 1 Pan
16 Pan = 1 Puraan
7 Puraan = 1 Silver coin
8 Silver coins = 1 Gold coin or called as Nishk (which was given in Dakshinaa to Braahman in Yagya)

In the Pratishthaa Yagya of large gardens, 2 Gold coins were given to Braahman as Dakshinaa
In digging well, 1/2 Gold coin (1 Nishk) was given as Dakshinaa
[Bhavishya Puraan, p 243-244]

My Note
At many places, many kinds of names are given, sometimes it is confusing, for example here it is written  1 gold coin was called Nishk, but below it is written 1/2 gold coin as Nishk.