Hello ;-)
The masteries for mysticism and magery are not that useful, unfortunately. Compared, for example, to Taming, Spellweaving and alike. While I think pricing is s very individual thing and I am one of the cheap sellers of stuff, I would say 500k might be ab appropriate price. If you play spellcasters, you would prefer weaving 3. With mystic-bards you would take the bardic 3, with ninjas the ninjitsu 3 and with hybrid-temps such as mystic-throwers the weapon 3.
Hope that helps.