Building a cheap drone flight controller, especially for a quadcopter with 4 motors, requires careful selection of components to balance cost and performance. Given your reference to the STM32F405RGT6TR microcontroller (MCU) in the project description, I'll assume you're considering this or similar MCUs for the heart of your flight controller. This choice is excellent due to its processing power, and availability of necessary peripherals. Here's a basic component list and some recommendations for a minimal yet functional flight controller:

For stable flight, at least two sensors are crucial: a gyroscope (for rotational movement measurement) and an accelerometer (for measuring acceleration and inclination). Many chips come as combined IMU (Inertial Measurement Unit) sensors which include both.

You'll need ESCs to control the speed of each motor based on PWM (Pulse Width Modulation) signals from the MCU. There are specific ESCs for drones that come with firmware that might include features like OneShot42/125, DShot, etc.

Choose brushless DC motors for your drone for efficiency and durability.

To add control or telemetry:

This setup provides a good starting point for a budget-friendly drone capable of stable flight, with potential for further expansion and enhancement based on specific needs or goals. Adjustments may be needed based on the exact requirements, size, and weight of the drone you're aiming to build.