This achievement sounds daunting but is not actually daunting at all. There are spoilers, but they're only applicable if you haven't yet completed the very first main mission "One Small Step."
You do not need 50 unique weapon mods. You can create the same modification 50 times (which is what I did.)
An easy opportunity to do this is right after arriving at
and there you will have access to a weapons bench.
*** Spoiler - click to reveal *** After entering, turn right and open the door to reveal stairs. Down the stairs you'll find a few workbenches (spacesuit, research terminal, etc.)
Simply go to the workbench there, find what available mods you have for your weapons. Identify the least expensive in terms of resources required. Identify how many you need. Save.
*** Spoiler - click to reveal ***Since the lodge is in Jemison, you can leave the lodge to the commercial district and purchase any required resources from UC Distribution or go to the spaceport and buy what you need from Jemison Mercantile.
After that, return to the workbench. Create the weapon mod then select no mod in the weapons modification menu. Then create the mod again. Then select no mod again. Repeat until the achievement pops. Return to your earlier save if you don't want to waste your money and resources.