You can find most of the best equipment inside treasure chests, so pretty much the only things that will become really expensive for the Fighter/Knights are the Mythril Swords in Elftown and the armor that costs 45,000 gil in Melmond. The former can be done with leveling up, especially if you use the Finger Point, and I usually don't get the armor in Melmond anyway since you'll get some better armor relatively soon.