Are there magic knives? No, but it depends on exactly what your needs are and what you're looking for.
As for price, it's all relative. Generally, the more expensive, the better the quality. However, sometimes we're paying extra for the name. The CQC6 comes to mind. IMHO, tools strictly for fighting need not be pretty or even a custom; it just has to work and work good. For that matter, in extreme circumstances, your tools can fail, they can be lost, or they can be confiscated after a fight. With that in mind, I've come to adopt the concept of expendability, looking for the least expensive knife possible without compromising the stringent requirements for a fighting knife.