To purchase all the abilities you need a lot of gold. The 2 most expensive abilities cost 99 999 and 88 000 alone. After I had completed the game and unlocked all other achievements I still needed almost 300 000 gold. The best method which unlocks 500 gold every 5-10 seconds is done the following way :
Step 1 : Choose the mission Auto-fab Plant
Step 2 : Equip the Photon Detonator
Step 3 : Play the stage as normal going past the first checkpoint. Do not destroy the object which gives the 5000 gold. Go past and get the 2nd checkpoint.
Step 4 : Run to the left and use
to shoot the Photon Detonator.
Step 5 : Collect the 5 gold coins.
Step 6 : Push Start , then push
to restart at the last checkpoint.
Step 7 : Rinse and repeat until you have enough gold to buy all Abilities.
Once you have gotten used to it you can earn 500 gold every 5-10 seconds.
After you have bought the last ability exit the menu and you will unlock the Ability Collector Achievement.DO NOT enable the All or Nothing ability as it removes checkpoints