Answer:

A Basic Upgrade Key is a code that may be used to activate Foxhound Version 5 as a Basic Edition copy after upgrading an existing copy of Foxhound 3 or 4.

The "Basic Upgrade" and "Extended Upgrade" prices apply to any previous edition of Foxhound (Rental, Basic, Extended). An existing Foxhound 3 or 5 database must be available to be read by the Foxhound 5 installation process.

You can purchase a Basic Upgrade Key here:

See also...
What is an "Extended Upgrade Key"?
What are the differences among the different editions of Foxhound: Rental, Basic and Extended?
What are the differences among all the activation keys?