Buy ‘serial to usb’ with Bitcoin Crypto-Currency – Spendabit

Brainboxes Industrial USB-C to RS-232 Serial Adapter

$37.05 at Scan Computers

USB to RS232 DB9 Serial Adapter Cable, 30cm, M/M from StarTech.com

$24.91 at Scan Computers

Adafruit WCH CH9102F Friend - USB to Serial Converter

$6.47 at The Pi Hut

USB-C CDC Serial Adaptor (5V)

$5.26 at The Pi Hut

Z TEK ZE552 USB 2.0 to 4 x RS232 Serial Adapter Cable Black (Cables & Adapters Category)

$75.95 at Gadgets Direct

FTDI Serial TTL-232 USB Cable

$19.95 at Adafruit

SparkFun Serial Basic Breakout - CH340C and USB-C

$14.02 at The Pi Hut

USB to Serial Adapter (RS-232)

$13.35 at The Pi Hut

Adafruit UPDI Friend - USB Serial UPDI Programmer

$9.03 at The Pi Hut

Olimex ESP-PROG-C USB to Serial Converter for ESP32/ESP8266

$7.56 at The Pi Hut

Adafruit CP2102N Friend - USB to Serial Converter

$7.82 at The Pi Hut

USB + Serial Backpack Kit with 16x2 RGB backlight positive LCD (Black on RGB)

$32.34 at The Pi Hut

Scan 1m USB-C to DB9 Serial Cable - Black

$13.45 at Scan Computers

StarTech.com PEXUSB312C3 2-Port PCIe USB 3.1 Card - 2 x USB-C - USB 3.1 Gen 2 - Up to 10Gbps

$64.99 at Newegg

USB-C CDC Serial Adaptor (3.3V)

$5.26 at The Pi Hut

USB to TTL Serial Cable Adapter for Hacking on Routers (TPE-USBSERIAL)

$8.99 at ThinkPenguin

StarTech.com NM9FF DB9 RS232 Serial Null Modem Adapter - F/F

$13.11 at Newegg

Serial Port 9 PIN DB9 / RS232 PCMCIA Expansion Card for Laptops (Laptop Accessories Category)

$40.95 at Gadgets Direct

USB to RS-232 adapter cable with COM Retention from StarTech.com

$35.02 at Scan Computers