Your Oracle Alexander/MMT set up is an extremely cost effective combo as it is, assuming that you have it is operating properly and set up well. You really won't get any kind of major improvement by getting a new tone arm. (I have owned this system for the past 10+ years and it competes with my Delphi, but doesn't best it).
Re phono stage, if you are going to get a MC cartridge be sure your phono stage allows you to adjust the load or matching cartridges will be a crap shoot. Personally I like the EAR 834P, but it might be a tad more costly than your budget.
In selecting a cartridge be sure to match the mass of the tone arm to the comnpliance of the cartridge. The MMT is a medium mass arm and your cartridge compliance should not be too high or low. FWIW I use a Micro Benz Glider on my Alexander.
Re phono stage, if you are going to get a MC cartridge be sure your phono stage allows you to adjust the load or matching cartridges will be a crap shoot. Personally I like the EAR 834P, but it might be a tad more costly than your budget.
In selecting a cartridge be sure to match the mass of the tone arm to the comnpliance of the cartridge. The MMT is a medium mass arm and your cartridge compliance should not be too high or low. FWIW I use a Micro Benz Glider on my Alexander.