Never been concerned with fair, as gil was/is so easy to get it really didn't matter. It all came down to how quickly I wanted something repaired. So what I'd do it offer 5-8k gil for something I wanted repaired right away, but only 1-2k gil for something that could wait.

For instance if I was playing my MRD and my Axe broke, but I still wanted to continue playing MRD and not another class, I'd go stand by the repair NPC in Ul'dah with a 7k offer and it'd get fixed within 3-10min every time, but the lesser not so important items for 1-2k would take a few hours.