I believe these are the easiest steps to get 777 Lei:
- Complete the game, and unlock the WCX in the
Extra Content Shop- In New Game+, meet the merchant and buy the WCX and Rifle Ammo Recipe
- Craft 1 Rifle Ammo
- Sell 1 Rifle Ammo to create a 7 at the end of your Lei
- Sell handgun ammo to create a 7 in the second last position of your Lei
- Make large purchases to get under 10,000
- Buy Handgun Ammo to create a 7 in the third last position of your Lei, and spend anything extra
- Achievement Unlocked