Using High Current ESC?

Roboteq makes this controller (SDC2150NS), which I think would be adequate for 48V, 1000W (ie, 20A) brushed DC motor:

http://www.roboteq.com/brushed-dc-motor-controllers/sdc2130-sdc2150-dual-20a-brushed-dc-motor-controller

It isn't cheap, though ($225.00 USD) - but you're not likely to find such brushed DC controllers to be so (not sure about BLDC).