Yeah I know. And there aren't any reversing car esc's that run on 6s or could turn the 16x10 prop since most car motor shafts are very small use for having a gear installed and have rather high kv. There are boat esc's that can handle the higher voltage of 6s, but, no way Im carrying a water fed system to keep the esc cool...that would require more weight then just putting brakes on the wheels.
The only other option really is to have the rear motor set from the get to turn in the direction to give opposite thrust and it would only function when you flip the switch. But then you're not getting the benefit of that motor during flight
So...looks like coughing up the $400 is my only recourse. BTW...a pcb board type device could be used as others have scratch made something and done it on rcgroups, but only on power systems of 3s or less.