This is not a complete guide, only a little help to get money for the non-hardcore GTA V gamers!
The key is money giveaway + ingame discount!
UPDATE: I got $750.000 on this way in 2 months (only 5 mins playtime). Events are very random, so be patient!
To start the Doomsday Heist DLC you will need a lot of money. That's not problem for hardcore GTA players, but what about regular achievement hunters like me and you? We spent only 60-80 hours in the game. I already completed every online achievement in the main game and original heist DLC, then bought a big house and some cars. Now have only $250.000... You can buy some Shark Cash Card through micro transactions or choose the very expensive Criminal Enterprise Starter Pack DLC.
There is an easy solution to get money without cheats and glitches! It's not need any playtime, but a lot of waiting, so if you want to do it fast this solution is not for you, sorry! You have to follow Rockstar Games on every social site (Facebook, Twitter etc.) and set https://socialclub.rockstargames.com/events/
as home page in your internet browser then wait for promotional money giveaway and discount days! Only a few events like this in a year!
For example: https://socialclub.rockstargames.com/events/C7oHeMP7/log-in-...
In this promotion players earned $1million in 5 days only for login! $250K for the first login then $150K every day until the last day of the promotion. Huge 40-50% discount on heist properties at the same time!
So you have to wait months before start this DLC meanwhile you can focus on other unfinished games!