[MPaulHolmes]

I now have a pretty good idea about what parts to use. There was a bit of trial and error, but that is gratefully now mostly over! There are several possible variations, but here is just one. This doesn't include the cost of shipping. Buying in bulk would really help to eliminate the cost of shipping, and would make the parts cheaper. Some of the component prices assume buying in modest bulk (say minimum of 10 or whatever).

Total cost of 144v 600amp controller without synchronous rectification:

MOSFETS: $5.59*12
DIODES: $2.36*12
RIPPLE CAPACITORS: $2.00*24
MOSFET DRIVERS: $1.95*2
POWER PCB: $0.80
CONTROL PCB: $2.00 (unsure at this point)
COPPER HEAT SPREADER: $28
ALUMINUM HEAT SINK: $25 (I don't know! Ben sent me his!)
COPPER BUS BARS: $9
ISOLATED 12V-12V DC TO DC CONVERTER: $15
BRASS NUTS AND BOLTS: $8
CURRENT SENSOR: $27 (You could get a $15 sensor if you had a band saw.)
MOSFET CLAMPS: $0.27*24
MISCELLANEOUS SMALL ELECTRONIC COMPONENTS: $20
SOLDER: $3
BOX FOR CONTROLLER: $20 (I have no idea! I still don't have one!)

ATMEGA8: $2

Total: $313.58



With Synchronous Rectification, you would need to add about $40, because you would need 24 mosfets, and no freewheel diodes, and would need a couple extra mosfet drivers and resistors.