Economy
The costs to fly your fleet is measured in supplies. That's supplies to regain CR (combat readiness) and supplies to do the daily maintenance. If you can't even pay the daily maintenance costs, your fleet will lose CR very quickly, and eventually accidents (low CR) will cause you to lose ships and cargo.
Rationing Supplies
The button to "Suspend Repairs" is very useful, since it can stop the large drain of supplies, and allow you to spend supplies on only daily maintenance, and so allows you to stretch a small number of supplies for a longish time. It would be wise to mothball or individually turn on "Repairs" for individual ships with very low combat readiness (for instance if they were hit by a storm), so that important ships are not lost to accidents. Accidents happen at random intervals to ships with very low CR. Or you can scrap your easily replaceable ships, and mothball the rest of your ships. You won't have any "Storage" if every ship is mothballed, but your maintenance costs in supplies will be zero. You'll still pay full price in hyperspace fuel though.
Exploring
Exploring the sector, you might take 200 times your daily usage in supplies, and 160% of the fuel you will need for a round-trip journey. The map has a "Fuel range" button. You can try and bring only 100% of the fuel needed, if you're fine coasting back with no control in hyperspace. The round trip radius doesn't count the fuel required to jump out of the destination system, or the fuel required to avoid hyperspace storms. The distress call button is always there, but you might only be offered 100 fuel, and really what you want to preserve is your fleet, not just one ship.
You can see your daily supply use by undocking, then hovering over the yellow supply readout, and pressing F1 to expand the data.
Selling ships
The insultingly low price the market offers for your ship, is very nearly the cost you pay in supplies to repair the ship after you find it in space.
Deployment costs
Deploying ships can indirectly incur a cost in supplies. For example, the Lasher frigate is one of the more economical combat ships. The Lasher loses 10% CR per deployment at minimum. This minimum cost corresponds to the minimum CR lost in any deployment. So, you'll lose 4 supplies to CR recovery for the Lasher alone-best case. If the Lasher goes down to very low CR, you'll spend much more on that Lasher alone-dwarfing the monthly supply cost for the Lasher. The Lasher is also notable for quickly regaining CR-other ships take much longer to regain CR. In fleet combat, the "Harry" option allows you to drain CR from the enemy fleet. This allows you to use the CR mechanics against the pirate baddies, and in actual battle they will find their ships malfunctioning, without shields or weapons, and you could win without firing a shot.
Since longer battle drain all your CR, please consider the expense to battle high-tech enemies, like an Falcon cruiser that snipes at you while running away.
Summary
- Bring 100 times your daily maintenance cost before undocking, or 200 times for combat missions.
- Battles are the main expense, for deployment and for replacing CR.
- When you think you're going to run out of supplies- Turn off repairs for the whole fleet, and then manually keep CR above 0 for each ship you intend to keep. This results in a gradual decline in CR for the whole fleet, while keeping daily costs at a minimum. This is to prevent the "no supplies" debuff, which quickly takes your fleet to 0 CR.
- Keep an eye on supplies after things happen. Hyperspace storms, solar flares, pulsars, black holes, Emergency burn- all of these can be expensive. The fleet screen shows the total cost to repair.
- If you recover a huge ship, consider mothballing it, since you'll only have to pay fuel costs. You can repair it once you get home.