I'd suggest a
Teensy 4.1 (about $27 USD), plus the
USB Host connector (about $3 USD, only need to solder standard 4-pin 0.1" spacing pin header). I also like to get the
Ethernet kit ($4 USD) just in case I want to use the hardware 10/100Mbit wired Ethernet connection also.
Note that you can connect the main USB connector to your development host while the barcode reader is connected to the Teensy USB Host connector, as long as the barcode reader doesn't require too much current (keeping the maximum current from the development host via the USB bus under 500mA). If using external power, note that the board does not have diodes, so you'll need to cut the VUSB trace (as described in the Teensy card) to make it externally powered only; or use an USB cable with the +5V line disconnected to connect the Teensy to your development machine while externally powered.
Of course, you'd need to port your Arduino project over to
Teensyduino, the add-on for Arduino for Teensy support. Biggest differences are in fast I/O port access (instead of PORTD etc., you use
digitalWriteFast(); like in standard Arduino,
digitalWrite() works too), interrupts, and timers: Teensyduino has easier interfaces for using all those.
Teensyduino developer, Paul Stoffregen, is a frequent contributor to Arduino (authored many common libraries et cetera), and I've found the
Teensy forums useful.
Oh, forgot. Teensy 4.x has 1,048,576 bytes of RAM, and can run at up to 600 MHz. (It's a really powerful Cortex-M7 microcontroller from NXP.) With one
PSRAM chip ($2 USD) soldered to SMD pads on the board, you can add 8 MiB of RAM; and you can use up to two of those PSRAM chips, if you find you need lots of RAM. This RAM appears as ordinary memory from address 0x70000000 upwards, so you can use it for your own data without worrying about bank switching or that kind of nonsense.
(I'm not affiliated, just a very satisfied and happy customer. I also occasionally help out on the forum there, too.)