In order to obtain this achievement you must purchase all of the items from the store (under character customization). From challenges alone you can get $910,000.
Club sets- $535,000
The best way that I found to acquire the necessary funds for this achievement was completing trials. Some notable trials are:
Willamette Pro Tour- score par or better on 20 courses=
Pitch and Putt Precision- score 20 hole-in-one's= $175,000
Shanking Through Shortcuts- score 20 birdies (complete the hole one stroke under par)= $110,000
Go to your Home- score 20 pars= $110,000
I Got This... Oops, Maybe Not- Score a bogey (hit one stroke over par)= $10,000
I found Pirates refuge to be the best course for this achievement. On this map you can get 2 hole-in-one's and 2 birdies/pars.
On the first hole aim for the middle tube and slightly lower your shot to 44 yards (still right under the middle tube). You should get a hole-in-one.
On the fourth hole look to your right and you will see a tube. Aim inside the tube and begin shooting when the tube's hatch just completely closes. By the time the golf ball approaches the tube it should be open. You should get a hole-in-one.
For the pirates refuge course you need to get a maximum of 13 strokes for par on the course.
You will also get $35,000 for purchasing 10 helmets, $35,000 for purchasing 10 golf balls, and $35,000 for purchasing 10 exo suits for a total of $105,000. You will also get $25,000 for killing 200 zombies and $30,000 for destroying 20 obstacles (tires and explosive barrels) for a total of $55,000.
Winning matches online (preferably boosting as few people play this game mode) will net you $100,000.
Right there, just in challenges you should get $790,000.
I found that the trial tastes like chicken and freedom- score 20 eagles= $110,000 is somewhat glitched. According to Krogan Warlords, eagles seem to only be obtained on the medieval town fairways on hole 1.
Remember that for the hole-in-one shots you must hit your swing in the green part of the shot bar.
As well, if you equip a golf ball, I used the electricity golf ball, and hit the sweet spot of the shot bar you will get a perfect shot and gain additional cash for any zombies killed (can net you $5,000 for the first hole for the pirates refuge course with the hole-in-one method). Hitting explosive barrels will also gain you additional cash for zombies killed.