That's a bit like the length of a piece of string
If you did a chainring you first need a digital vector drawing of the logo and lettering to create a plot file for the CNC. Then you need a jig for the chainring so it can't move. The CNC's have vacuum beds but I wouldn't trust it to hold a chainring. So its probably around £70-£90 before you start. I've been tempted to try one but not got around to it. Also, I'm not sure I'd risk a Campagnolo ring first hit!!
A stem would be a whole other ball game. It sounds like ph billet knows more about floating heads and 3d routing. Again, you could have a few nervous moments watching the bit head towards that nice polished Cinelli stem
I bet somewhere in deepest Poland a few months ago, a certain eBayer researched using a CNC and thought 'stuff that it sounds a bit of a faff - I've got a steady hand' and the rest is history.....