reducing item condition depreciation

[Enkidoh]

There is also Free Company buffs for FC members that do reduce gear degredation, specifically 'Proper Care' and 'Proper Care II', which slow the rate of gear degredation by 10 and 20% respectively for 24 hours.

You can get these buffs as long as you are in a Free Company and the company owner or a member with the required permissions purchases and sets the actions.

It should be noted that gear wears out at different rates depending on if you are in the overworld or in instanced duty -equipped gear in dungeons, trials and raids degrades at a much faster rate than normal fights out in the open world, so it may pay to get into the habit of regularly visiting a NPC repairer between duties, as otherwise it's very easy to quickly end up with badly degraded gear that will cost a small fortune to repair.

[Iscah]

It should be noted that gear wears out at different rates depending on if you are in the overworld or in instanced duty -equipped gear in dungeons, trials and raids degrades at a much faster rate than normal fights out in the open world, so it may pay to get into the habit of regularly visiting a NPC repairer between duties, as otherwise it's very easy to quickly end up with badly degraded gear that will cost a small fortune to repair.

Are repairs more expensive if the gear is in worse condition, or is it a "fixed cost per percentage point restored" deal?

[Sove92]

Are repairs more expensive if the gear is in worse condition, or is it a "fixed cost per percentage point restored" deal?

It's 5 gil per percent restored for lv70 gear but the cost also considers the sub-percentage, so you can get costs like 293 gil.