I've always made my own kits. But then, I was an ambulance paramedic for many many years (expired/retired now).

You can save money by not buying tons of sterile dressings. A few sterile 4x4's backed up with some sealed packages (but not sterile) 4x4's can save some money. Back in the days when I worked on an ambulance, we had Kling and Kerlix for bandaging materials (everybody hated the Kling, but it was much cheaper than Kerlix). Now-a-days there's this neat stuff called Coban. You will go broke trying to buy much of that stuff from a pharmacy. Buy it from an online horse supply store instead. 1/4 the price for the same stuff, and it comes in more cool colors and sizes for horses! And those individual packs of Tylenol or Advil doses that come in pre-made first aid kits are expensive. I just use a very small bottle and stuff it with my own Tylenol and Advil (and Benedril and Sudafed, etc.) You're not supposed to mix meds together in the same bottle - I always told my patients that - but of course I do it myself. The day I can't tell a Tylenol from an Advil from a Sudafed by looking at them is the day I shouldn't be wandering out into the wilderness anymore either.