First off, hello everyone. I've been a long time lurker and finally decided to register on the forums. I have built a 3D printer (a RepRap) and now have the CNC bug. I'm trying to hobble together a PCB mill using junk parts (just to make it a challenge) and I stumbled across this thread. I'm going to be using an RC brushless motor for my setup. Now that the introductions are over, on to the topic at hand.
Here is a thought, why not use a computer power supply? A lot of the high end computer power supplies are capable of supplying such amperages. Most of them have active PFC and are designed around extended periods of use. It is a trivial matter to jumper them on. All you need is a paper clip and a junk hard drive to partially load the 5v and 12v rails while the main motor is off.
Here is an example of one that can supply 60A on the 12v rail for ~$100