David:
If you have access to an ADD Player's Handbook, check there.  However,
here's a quick summary from the 2nd edition.
 
Cat = 1 sp, Trained Jauguar = 5000 gp
Pig = 3 gp, Trained Falcon  = 1000 gp
 
I'm not a DM but .. if the ferret was trained to hunt or steal, probably
500-750 gp (If you could get 'em to fly, triple it!  Who needs a falcon
anyway?).  Hired trainers probably would be 10-30 gp/year.  Better to try
to attract a henchman with experience.
 
Good luck!
 
Megan and Monster
[Posted in FML issue 1602]