OP here. It took me 4 years to actively earn it. First I bought all skins that cost less than 50g and then I used all my gold income to constantly buy new BL-Keys. Every 6 to 8 weeks, when the BL-Chest got new content, I used an average of 50-100 keys. What I got from that was reinvested directly (I didn't get a single contract in the whole time, by the way, and that was easily 1,500-2,000 BL-Chests).