Taken from Techobots web site.

4QD pro 120s £130 Each + 4QD mixer £42.53
Total: £302.53
RoboTech £395.95

What isnt clear is if you need failsafes for the 4QD mixer and this is the cheapest configuration that will work.

So for just an extra 23% cost you get the best out there so far. Its simple to wire up, only one box + Rx and has builtin failsafes and more functions than any other contoller out there. Oh and its lighter!

Your choice. If you want really cheap then you could even make your own (check out OSMC in google) but if it doesnt work first time it will probably end up costing more.