The Thunderbolt (2) to Firewire (800) is available for $34.89 at Staples. I've had one for several years. I used it to connect my Saffire Pro 24 to the integrated Thunderbolt port in my Asus motherboard. It worked great in Win 8.1 as well as Win 10.
I have since acquired an Antelope Audio Orion 32+ which works fine with their new Thunderbolt for Windows driver. I currently choose to use the USB driver because it allows multiple apps while the Thunderbolt driver only allows one app at a time.