Regarding the 4QD, i have used them in the past but they are bulky and in the case of the PRO 360, expensive. As for the Vex BB controllers, they are again expensive ($499 each) and are not easily bought in the UK anymore.

Your best bet would be to look at the Roboteq controllers, there are plenty of builders who use them so plenty of people who can help with them, they are also available as dual channel and single channel controllers so you can choose if you want 1 controller or have 1 per motor.
Another option would be the Robot Power Vyper: https://www.robotshop.com/uk/vyper-1...ontroller.html
you would need 2 for drive and you would be limited to 36V but then you would need 2 4QD controllers as well or 2 Vex BBs.