Option 1: Make use of Bulk Copy Functionality under Version Settings. Create a Version called "Frozen Budget", use Bulk Copy Functionality and snapshot the data from Existing Budget Versions to Frozen Budget Version. Note: This is an admin activity and cannot be published on to the dashboard. Also Adding version will have an impact on the overall size of the model
Option 2: You can use DCA on the modules along with Formula Scope but this requires a considerable amount of effort. I would keep that as my last option.
Hope this helps
Misbah