The Maker Pi RP2040 is a particularly inexpensive developer board that is suitable for realising your own robotics projects. The Maker Pi goes for US$9.90 and features numerous connections.
https://www.notebookcheck.net/Cytron-launches-the-Maker-Pi-RP2040-a-cheap-developer-board-with-a-Raspberry-Pi-microcontroller.552001.0.html