Go to System>Tools>Category Editor
In the drop down box find the Price Qualifier category
Find the Price Qualifier you require from the list and tick the box
If the lead source does not exist then send a request to Support for inclusion. However, you do need to check that portals etc will accept price qualifiers that are out of the ordinary. In particular Rightmove have a very limited choice and may change your choice to fit their system
The order of the sources can be amended by using the ‘+’ and ‘-‘ keys