Hmm it depends, first off what kind of knife are you looking for? Flip Knives, Falchion Knives, and gut knives are typically on the cheaper side. Cheaper patterns are Forest DDPAT, Boreal Forest, Stained, and urban masked. I know there are some more but cant think of them off the top of my head.
Gut knife is the cheapest and you can get some cool patterns like Doppler or fade for relatively cheap. Gut knife fade actually looks pretty decent too.