Power supply is tricky (unless you have a large budget) since 70 amps is a pretty large current:

http://www.ebay.co.uk/itm/HOT-Univer...ht_2890wt_1037

£40 for 20A .. not great, but there's another way. If you place a battery which can deliver the peak load in parallel with the ESC&PSU then the PSU only needs to supply the average current. This is where it's easiest to just measure how much current the motor draws when cutting and get the PSU to match. A standard multimeter wont measure 70 amps since they tend to be fused at 10-20A. Something like this is excellent as you can measure the current and it records the peak current:

http://www.hobbyking.com/hobbyking/s...Analyzer_.html

Or the cheap way is to use a multimeter to measure voltage across shunt resistor, which can just be a short length of wire of known resistance. I used one of the following batteries, with a 0-50V, 0-20A lab PSU in parallel on mine:

http://www.hobbyking.com/hobbyking/s..._Rex_500_.html

That battery is rated for 60A constant, or 90A for 10 seconds which is plenty. Since my PSU has variable voltage output and current limiting I can set it to just below the fully charged voltage of the battery (i.e. <22.2*4.2) and it will never overcharge the battery, which is very important since overcharging a lipo battery is a good way to start a fire. So whatever PSU you get if you decide to use in combination with a battery will need to have good stable voltage regulation below 25.2V. Two computer ATX PSUs in series is nice and cheap and will give very close to 24V, however it is CRITICAL to ensure they are electrically isolated before putting them in series. The battery would never fully charge, but that's a good thing if anything as it increases it's life expectancy. You could get the battery first, use it to power the motor to measure the current then buy a PSU to suit.

We can estimate what power you require; what cutter diameter and depth of cut do you generally use (at 2.5m/min presumably)?

For example:

12mm cutter, 2.5m/min and 60% stepover at 6mm depth of cut is 108cm^3/min material removal rate (12*0.6*2.5*6=108). That's about 740W required...and a pretty rigid machine to sustain that. So you'd ideally want a PSU rated for a bit more than that to be safe. Also it's a good idea to put better capacitors on the ESC, especially with such long wires, to reduce the impedance...

Hopefully it'll turn out the motor draws a lot less current and you can just use a standard PSU.