Same product with different cost

Rajesh PB (80 Points)

30 July 2017  

Im manufacturing jewellery, 

I buy the metal and manfucature it , depends upon clinets requirement of purity.

So the rate goes different for per unit, depends upon the purity.

I mention jewelery unity price 30 rs in an invoice,

Jewellery 40 rs in another invoice.

Can i do like this?

Or need to mention purity?