The best cutting and squaring method??

Hey all..

I have ordered many pieces of V-Slot from openbuilds, but unfortunately I have received rail of different length.
So to explain, I have three pieces of 20X20X500mm but all three pieces are not the same length, and the difference is up to 2mm between them.. I have also received other widths of multiple lengths..
mostly the difference is just in the 1/2mm to 2mm range..

This is causing several squaring issues..

So my question is: What would be the best, yet not too expensive...

The best cutting and squaring method??