I've noticed that in analog signal acquisition hardware you see two paradigms: AC-coupled and DC-coupled. Typically AC-coupled hardware is less expensive, and basically has a 20 Hz high-pass filter to remove the DC component. DC-coupled hardware, which is good for reading sensor signals for example, tends to be in the hundreds or thousands of dollars, whereas AC-coupled hardware like computer sound cards is very inexpensive.
What are the electrical challenges in designing high-quality circuits for sampling DC-frequency analog signals? I'm trying to understand why there is this huge difference in cost.