Presuming that this is going to be entirely IC stuff and not using in-game ranks, then here is my suggestion, bearing in mind that this is a more SL-famaliar concept.
Since HP is not a considered factor, then the rank of jutsu is purely based on the complexity and the amount of chakra required to perform it. The two are proportional and also independent; a fairly complex jutsu may not require much chakra, but still be a relatively high rank. Hence, the chakra subtraction is based entirely on how much chakra is required, the complexity hindering accessibility for ranks.
This is about where the SL chakra system (however broken it may be) looks like currently:
Chakra Capacity:
E 4-7
D 8-15
C 16-31
B 32-63
A 64-127
S 128-255
SS 256 - Over 9000!
vs Jutsu Costs:
E 1
D 2
C 4
B 8
A 16
S 32
SS 32 (yes, I notice that it is the same as S, that is the joke)
Yes, you're reading that right, someone with supposedly B-ranked chakra capacity, at the top tier for that level, can spit out 1 S ranked technique OR 1 SS ranked technique, the difference being biju bomb lazer to biju bomb nuke, but someone with SS-ranked chakra capacity (most of the shinobilegends of the realm) can spit out a minimum (not maximum) of 8 SS ranked jutsu, while an Edo Tensei (the legit over 9000) or someone with crazy enhancements (let's say 511 for hypothetical reasons) can pretty much go an entire standard fight using only SS-ranked techniques, not to even mention the meager lessers.
The people with lower chakra levels tend to cap themselves more, while those with greater amounts kind of just let loose on what is reasonable.
A modified system that doesn't entirely neuter the system, but brings it more down to earth levels:
Chakra Capacity:
E 4-7
D 8-15
C 16-31
B 32-63
A 64-127
S 128-256
SS 256- OO (infinity, only for tailed beasts and Edo Tensei zombies)
vs Jutsu Costs:
E 1
D 2
C 4
B 8
A 16
S 32
SS 64
This would have have people of said chakra ranks performing approximately 4 jutsu of their chakra rank but none of a rank higher than. This is completely and utterly base: no enhancements, no reductions due to specialties or "great chakra control" (whatever that means in SL language), just a Kakashi-esque character who has no chakra boosting capabilities but is efficient enough in chakra control not to waste a great amount of chakra performing moves.
How would one progress through these chakra levels you might ask? Haven't gotten that far yet, but this is my idea, just to revitalize this thread.
* PS: I am aware that is very similar to Raifudo's in execution. Also noticed I was totally wrong on my math, E ranked folks can use up to a C-rank technique plus a few lesssers, for example.