You have the basic idea. No idea where you’re getting $9.50 from. Total cost per channel should be under $1. If you’re having trouble finding optocouplers, look up the 4N26. [These guys probably have everything you need, and cheap.
The reason for logic is that you want the on->off transition to pulse one output (for a pushbutton), and the off->on transition to pulse a different one. One toggle for two pushbuttons was what I think you asked about. An SPST switch is fine.](http://www.bgmicro.com)