RC Low-Pass Filter Design

I need a clean, passive low-pass filter designed around standard resistor-capacitor (RC) components. The target cutoff is comfortably below 1 kHz, so I expect calculations that clearly show the ‑3 dB point in that region and justify the chosen values... (Budget: $10 - $1000 USD, Jobs: Analog Electronics, Circuit Design, Electrical Engineering, Electronics, Engineering, Mechanical Engineering, Signal Processing, Technical Documentation)