I possess many knives. Many are Balisongs. Custom handmade Balisongs run $450+++. Production Balisongs are made in smaller quantities or are discontinued so they are also costly. Most have materials that are difficult to work with such as titanium and most have higher grade steel that retains edges longer.
Others are automatic knives like a Microtech Combat Troodon or multilayered San Mai Steel knives like my Cold Steel Master Tanto and MCUSTA Katana.
Workmanship and materials are the key factors that make a knife cost a bit.