You can fly infinitely with three maxed out bug drives (Even a little less than maxed out works actually). A jet with the three drives costs just over a million dollars.
Tip: For quick money and/or bp get the interest and daily bp upgrades in the bonus shop. This works best if you have interest at level 2, so get that first and the bp one later. Sell all your stuff, and just keep dying. The amount of money you get should be decent (If you have 10,000 money, you get 200 every day) and this amount will increase every day. You will eventually get around 1000 money each day, just for falling down. You will also accumulate BP while doing this.
Some tips for late game:
When you buy the nexus, DO NOT do any spells. Instead, build another nexus. Energy is generated at a rate of 0.1 per second, so it takes forever to do anything if you don't build another nexus. I learned this the hard way
This was a creative idea, and had all the aspects of a great puzzle game. It was simple, the levels were a solvable difficulty, it truly was minimalist. There is only one problem - Make a mouse on the screen! Because of that, I give it 9/10. Still, it is a great game.
in level 8 I accidentally stuck a Dibble between the step and under the ledge. All the others just left without him, but he was still alive. I was almost crying. The level never finished, though.
 "Learn to Fly 3"){kind=icon}
 "Swarm Simulator"){kind=icon}
 "Tesla: War Of Currents"){kind=icon}
 "Momentum"){kind=icon}
 "Cargo Bridge"){kind=icon}
 "Zombo Buster"){kind=icon}
 "My Little Army"){kind=icon}
 "Incursion 2: The Artifact"){kind=icon}
 "Incursion"){kind=icon}
 "Ragdoll Achievement 2"){kind=icon}
 "Socrates Jones: Pro Philosopher"){kind=icon}
 "Dibbles 2: Winter Woes"){kind=icon}
 "Cursed Treasure 2"){kind=icon}
"Turning LtF3 into an idle game 101". But heh, if you like it and it works, why not? :P