Obtaining 1000 coins is a fairly easy task. Because the mode is exactly the same as a normal run, with the only difference being coins, slots, and vending machines, you can horde coins until you hit 1000.
If you are feeling risky however, all slots have 3 coin payouts of a different amount. Before the last update, those amounts were 5-10, 10-20, 20-30
For a guide on getting to level 50 without using coins, please refer to my guide here: