There is a way you can get an unlimited amount of rare, purple mods early on in the game that will help you progress faster. You will be able to do this during the 'A Seeker at the Gates' quest. Locate the campfire that is just northwest from your starting location. Once there, go further west following the river and you'll find the Scrapper Site where you'll need to stealthily kill the Scrappers and collect their rare mods. After that, go back to the campfire, save the game and quit. Once you start the game again, you'll be able to do the looting again and, eventually, get the infinite amount of rare mods to sell or use.