Today Atmel, Microchip and others make inexpensive microcontrollers with native USB peripherals. The Atmel "8u2" chip, for example, is less expensive than even most of the FTDI clones, and certainly a LOT less than a genuine FTDI chip.
For years, I've published a very simple and easy-to-use USB code for those chips.
I also publish a signed INF installer that works with ALL USB Serial based on this standard protocol (called Communications Device Class, Abstract Control Model, or CDC-ACM). All 3 operating systems have the necessary driver built in. Mac OS-X and Linux load it automatically. Windows needs the user to add a INF.
Sadly, the CDC-ACM driver in Windows (called USBSER.SYS) is buggy. About a year ago, I sent Microsoft this reproducible bug report.
In a follow up email a few months ago, they were supposedly testing a fix. I'm hopeful that Windows 10 may be the first version of Windows to ever ship with a good quality USB Serial driver (as Linux has done for many years, and Apple as done since releasing Lion a few years ago).