I'm a big Kennametal fan. I don't know if it's nationwide or just locally, but they're very aggressive with making great deals. Through Tool Crib, we can purchase a batch of 10 inserts and get a free holder, half the time I don't even need to ask for the holder.
As far as manual vs. CNC, like others said, the biggest thing is RPM. The other is power. You may have better luck using more positive geometry on a manual, for less cutting force. We use the same inserts on CNC or manual - less inventory that way... in a job shop environment, when you may run a stainless job after a tool steel job after an aluminum job, you would waste a lot of time and inventory trying to "optimize" even for these three main groups.
I will say, one insert I know that works great on less-beefy machines (our Haas CNCs and manual lathes) is by Ingersoll, it is a DNMG 432 VF-TT9080. Very large chipbreaker, cuts quite freely and yet it will take a cut. .125 to .150 per side at .012/rev. Whatever speed you want, 400, 500, 700 FPM even, if you have coolant... and they're cheap! I get mine for about $10 per insert.