Connecting a FireWire 800 external hard drive to MacBook Pro early 2013 through its USB 2 port

The Apple Thunderbolt to Firewire adapter is $29, and I don’t think you’ll find much cheaper that that for adapter cables. However if the external Firewire drive is just a normal drive in a Firewire enclosure then you could pull the drive from it and use either a USB3 hard drive case or even a laptop hard drive SATA to USB3 cable. Those cables and enclosures start at around the $10 mark on big ecommerce sites.

Unfortunately there are no USB to FireWire 800 adapters.

FireWire and USB use different protocols thus an adapter could not transfer any data.

Unless you use some kind of Thunderbolt dock you will need to get your hands on a Thunderbolt to FireWire 800 adapter.