I wouldn't buy a power tool for a single chassis. I've found that with a little patience, hand saws produce a very good result. A hack saw can make a very straight cut if you follow a straight line with the saw at a long angle - the blade itself keeps you cutting straight. A finer-blade saw can make nice round cuts:
http://www.rc-monster.com/forum/show...8&postcount=54
I've had to do very little filing/sanding when I'm done.