Here is my resource saving Unryuu farming composition. Keep in mind that it is only viable if you retreat after node J.
Carrier Task Force.
Main fleet: 1CA(V), 1BB(V), 2-3CV(L), 1SS
Escort fleet: 1CL, 1CLT, 2-3DD, 1 SS
Put the minimum number of fighters on your CV(L) to achieve air supremacy. Add a Saiun (recommended) and a Type 2 Recon Aircraft (optional) and load the rest of the slots up with bombers.
You can use low level DDs in the escort fleet, since they won't really have much of a chance to do anything.
Either use low level SS for both fleets, or have enough SS in reserve to rotate. The SS are there to tank and will save you from annoying scratch damage on other ships in the long term.
You can have less than 6 ships in each fleet for a combined fleet. If you go with the lowest consumption ships (i.e. CVL rather than CV) and only 5 ships per fleet, you are looking at around a ~150 fuel and ammo cost per run.
The downside to this method is that your ships will get fatigued after around 2 runs, so you either need to wait for them to recover or swap them out with other ships.