Plugin for specific user privileges on fields

[hakim]

Hi folks,
I need to make a plugin that allows to set user privileges on specific fields when creating the class.
For exemple, when adding a new text input or a textarea to a class, I would like to make a new layout under "Settings(input)", which will allow to choose a usergroup, and attribute to it the needed privileges (r, w, or rw),
A little example: the price field can be changed only by the "Accouting" usergroup.
I need to do this using a plugin because I want to to be reusable.
Any hints on how that can be done?

Cheers.