I've got an order entry system in Filemaker 8.5. Each order has a status. After the status is changed to "billed", I'd like to be able to lock the record so it is viewable only and cannot be edited.

I do have 2 privilege sets created -- Staff and Admin. I'd like the Admin to be able to still edit the record if necessary, but it to be totally locked by the Staff.

Is there a way to lock the record based on the status of the order?

Yes. Use a record level access calc. In the Staff privilege set, set the edit capability to only allow edit if status ≠ "billed".

You may also consider a second layout for an order, a "locked" layout. Navigate to this layout when the status = billed. The fields on this layout do not allow enter in browse mode. Coupled with the rla calc, you've protected the data from edit.