High Guard presents differences between the TL 9 Jump-1 drive and the TL 15 Jump 1 drive.
IIRC, they get smaller and more expensive for a few TLs and the drop in cost at each higher TL ... [going to look it up] ...
... [Here it is: High Guard, p.52-53]
So from the Core Rulebook, J-Drive A is 10 dTons and MCr 10.
From High Guard, that would be TL 9 for a Standard J1 capable J-Drive A (10 dTons, MCr 10).
From High Guard, I could "improve" that up to a TL 12 J1 capable J-Drive A (7.5 dTons, MCr 20).
High Guard (pg 52) also states:
There is a 5% price discount per TL for older technology devices if bought new at the source, to a maximum of –30%.
Therefore, from High Guard, I could purchase a TL 12 version J1 capable J-Drive A manufactured at TL 15 at a 15% discount (7.5 dTons, MCr 17) or a TL 9 version J1 capable J-Drive A manufactured at TL 15 at a 30% discount (10 dTons, MCr 7).
It has been suggested that the "JD Fuel" is not fuel in the traditional sense, since the energy released by fusing tons of hydrogen is staggering and would melt the ship at anything below 100% efficiency, so a bubble of hydrogen around the ship to insulate it from Jump Space is a common technobable explanation. If this is the case, then jump fuel is more like displacement in a wet navy ship ... a 100 displacement ton wooden ship in 1800, displaces exactly the same volume of water as a 100 displacement ton racing boat in 2015. Displacement does not change with TL, and neither does the Jump Bubble. [shrug ... at least that's the common argument].
If you want to change JD fuel volume, I suggest really shaking things up and swapping MD Fuel for JD Fuel.
JD Fuel = 1% per Jump Number (to power a JD)
MD Fuel = 10% per Gee (reaction Mass for a fusion torch)
It is still all handwave magic technology, but it is a step closer to reality.