Get ( accountname ) can identify an individual user and get ( acccountprivlegesetname ) can identify groups of users.
You thus can use such info to look up the ID of the user's company and put it in a global field or variable when the file is first opened. This will require either a field in T1 that lists a single account name or privilege set or you'd need a new, related table of account names for multiple users from the same company.
Then your calculation can compute different prices based on the company. There's more than one way to do this. If Markup Percentage is the value that determines company specific pricing, you can put the company ID in a global field used in a relationship to match to a company record then your calculation can refer to the field via this relationship. When a user from a different company logs on, the relationship matches to a different record and a different selling price is computed.
Your relationship might be:
T2::gCurrentCompanyID = T1::unique ID
and then your selling price calculation in T2 might look something like this:
ItemCost * T1::Markup Percentage + ItemCost