I was able to locate a free option on the F150 forums when I had my F150. Someone figured out the pinout wiring of the disable switch. They suggested that you jumper two pins from the back side of the switch. At every start, the truck got the signal that the button was pushed and it disabled start/stop. I had this on my truck until the day I turned it in. It was a 10 minute job, so paying $99 was not worth the cost to me.
I don't have start/stop on my Rebel, but I hated it in the summer in Florida. Around Orlando, the government must have a large relationship with the gas companies for the tax dollars, so they set up lights every 10' it seems. I would sit at lights or in stop and go traffic so much, that the AC would cause the truck to start and stop during a single light cycle. It became annoying.