Many simple Arduino clones skip the on-board USB to Serial conversion and just include a 6-pin header for a $20 FTDI cable. If you want to save money you can find some $3 cellphone USB cables that do the USB to TTL Serial conversion. Many of those use the 3.3v LVTTL logic levels so be sure to get one that matches your operating voltage.
The main disadvantage of those cheap serial cables is that they don't bring out the DTR signal wire used to perform the auto reset function that the arduino IDE uses to activate the bootloader at the correct time. You can master performing a manual reset but it takes practice to learn the correct timing for that operation. Also finding the proper USB driver for some of those serial cables can be a problem depending on the OS version you have.