Honestly the cheapest board you find of amazon or ebay. maybe this kit https://www.amazon.com/REXQualis-Development-Membrane-Receiver-Detailed/dp/B074WMHLQ4/ or just the board alone https://www.ebay.com/itm/Arduino-UNO-R3-Mini-Micro-USB-ATmega328P-CH340G-Replace-ATmega16U2-Board/201927954809

If you're familiar with Processing or Wiring, the Arduino IDE & ecosystem is a clone of that just as the random items i linked are clones of Arduino and inter-compatible