I started with pre made kits. And then I realized that nearly any premade kit below 50 bucks suck. Pretty much all of them are lacking on gauze and various compression wraps.
One of the most important things you can buy is rolled gauze, preferably kerlix, or compressed gauze. It doesnt take much space, it isnt expensive, it isnt heavy, and is used for a lot of things. Add a bunch of gauze to a kit, and you can deal with a wide variety of problems.
What is your focus? General first aid? Trauma/gunshot wounds? Your focus will determine how much you have to shell out.
Also, I would avoid quickclot sponges. It isnt worth the money in my book. They aren't much good for penetrating wounds, and you probably wont need QC for lacerations or cuts. Gauze, ABD pads, and direct pressure can solve almost all bleeding issues. If that doesnt work, it's probably time to consider a tourniquet. If you want a hemostatic agent, celox is the best. It creates a gel inside the wound, and doesnt leave much behind to cause problems down the road, unlike QC granules, which can be extremely dangerous if left in. Also, treating trauma is very complicated. But there are some basic supplies that can help a whole lot, and dont require a ton of know how.