You can update your firmware using an FTDI breakout instead of the expensive cable. These are inexpensive USB->serial converters commonly used for programming embedded devices, and I suspect the same chipset is what is in the OEM cable. I'm a tinkerer/electronics hobbiest and I have half a dozen laying around. I was able to update my firmware using the this module and some generic female/female jumper wires (dupont cables). The pinout on the CP1 is GND (indicated by a triangle on the board) RX TX VCC (3.3v). You just need to connect GND to GND on the breakout, RX on the panel to TX on the breakout, TX on the panel to RX on the breakout. VCC doesn't need to be connected.
Obviously this method isn't for everyone, but if you're somewhat technically inclined, it can save you money on a cable. If you're already into electronics as a hobby, then you likely have the parts laying around already like I did. Was able to update my Vivint panel to 1.14 then roll back to 1.13 to clear lockout and gain installer access.