How do I get high-performance guitar microphone going for cheap?
The key aspects of high-quality microphones include:


Frequency Response: In many cases flatter is better, but many high-end microphones are selected for particular applications precisely because their responses are not flat. They might have just the right amount of high-end or low-end rolloff, or have a midrange boost in just the right place.
Pickup Pattern: You have a choice of pickup patterns ranging from omnidirectional, to figure-8, to cardioids and super-cardioids. For the non-omnis, the off-axis frequency response can vary quite a bit from design to design. Again, this makes different microphones better for different situations.
Sensitivity and Dynamic Range: It's difficult to produce a microphone that has good sensitivity for soft sounds while also having the robustness to handle loud ones. You'll use different models depending on the type of sound you're expecting.
Noise: Especially if a microphone has an active preamp, the noise floor can become the limiting factor on the dynamic range.
Physical Robustness: You wouldn't take your best studio microphone and give it to a singer to hand-hold in a live concert.


It would be difficult to achieve good scores in all of these areas with an array of cheap microphone cartidges, for a number of reasons.