What is the best MM or Hi Output MC cart for $250?

I have an older Rega Planar 3 TT with an Accutex MM cartridge and a Bellari VP129 MM phono stage and think I may be overdue for a new cartridge. It still sounds very good, but how do you know when its time for a new cartridge and what is the best one that would work with the Bellari MM phono stage for $250 or less?
Thanks for your replies.
Louis