I just noticed the Axiom lite and the GM2000 are going for the same price. I don't know a lot about metal detectors, but I was led to believe that the PI machine is always superior.
It is my understanding GM2000 is better at detecting fine/small gold and easier to learn, Axiom is deeper and better in hot (highly mineralized) ground but more difficult for inexperienced people.
Minelab Gold Monster 2000, Manticore, Nokta Legend 2, Magnetar 9000, XP Deus 2, FTP Tek Point, Nokta Accupoint, Gold Hog River Sluices and Flow Pan, Royal Mini High Banker.