Artillery range & shooting speed technologies have inconsistent costs as you move upward:
Level 1: 3500
Level 2: 14000
Level 3: 3500
Level 4: 14000
Level 5: 3500
Level 6: 14000
Level 7: 31500
These should ramp up consistently like other infinite techs.
Turns out, this isn't just limited to artillery - refined flammables does the same thing:
Level 7: 3000
Level 8: 12000
Level 9: 27000
Level 10: 48000
Level 11: 3000
Level 12: 12000
Level 13: 27000
Level 14: 48000
Level 15: 75000
Level 16: 3000
Level 17: 12000This might make sense if you consider the fact that you're adding new tech cards, but the numbers get to ridiculously high levels.
This will require more investigation, as it could be happening to other infinite techs as well.