How to add new column to sales invoice items

Hello everyone,

as a “supplier” i want to sale Computer to other company
but i want them to sale that computer with a Public Price
so
i want to sale computer to:

  • Company A with 1000$ but they should sale it with 15000$ not more not less
  • Company B with 950$ but they should sale it with 15000$ not more not less
  • Company C with 900$ but they should sale it with 15000$ not more not less

with price list i can do the first part ( 1000$, 950$, 900$)

but i try everything with the second part without any success
i want that any Item had new field named : Public Price
and any time i select any item in sales invoice for example i want that “Public Price” to be showing close to Quantity field
i want something like this:
| Item code | Item | Qty | Public Price | Price | Total
| AA--------| AAA | 10–| 1500---------| 950| 9500

sorry for my English
and thank you for your help