sorry about all the nitpicking of your rules. but the double amount of current ic needed is kinda harsh. Since you're only making 1 more ic per turn it'll take 4X amount of turns(x being the starting ic. 2->3 takes 8 turns. 5->6 takes 40 turns etc) until you've made back that much money.
So say I make 4 per turn. It'll take two turns to get to +5. So lets start from 2 turns. The +5 now starts at -8(since you had to spend that to get to 5. Basically wasting money that could be used on say infantry) while the +4 starts at 8(your net gain regardless if you spent it on something else since you werent 'wasting' it).
Turn 0: -8, 8
Turn 1: -3, 12
Turn 2: 2, 16
Turn 3: 7, 20
Turn 4: 12, 24
Turn 5: 17, 28
Turn 6: 22, 32
Turn 7: 27, 36
Turn 8: 32, 40
Turn 9: 37, 44
Turn 10: 42, 48
Turn 11: 47, 52
Turn 12: 52, 56
Turn 13: 57, 60
Turn 14: 62, 64
Turn 15: 67, 68
Turn 16: 72, 72
16 TURNS!
Lets even bring the numbers down to 1 and two.
Turn 0: -2, 2
Turn 1: 0, 3
Turn 2: 2, 4
Turn 3: 4, 5
Turn 4: 6, 6
Even this minimal gain for the poorest of nations would take too long to gain back what they spent.