I have a problem that when i create a standard user for making offers i don't want him to access any purchase or cost prices how could i do this ?

You can limit the standard user's access in your QuickBooks Online (QBO) account, @andrewnarooz. Let me share further details about this.

When you create a standard user in QBO, you can set different levels of access. They can work with customers, sales, suppliers, and expenses. Since you don't want them to access any purchase or cost prices, you can select either the None or Limited option in the Select access rights page once you're ready to add the new user. (Please see the screenshot below).

For the complete description of what a standard user can and can't do in your QBO account, kindly check out this article's Types of billable users (Standard user) section: User types and user permissions in QuickBooks Online.

You have the authority to change what a user can do and see in your QBO account. To effectively manage the user access in QuickBooks, I'd recommend checking out this article: Change user access. It also includes steps on how to add and delete a QBO user.

Please let me know if you have other concerns. I'm just around to help. Take care always.