oooooooooohhhhhhhhh ok I see what you mean.
I have in the past controlled LED's directly from my serial port, but there are issues with that:
Not enough I/O to control more than 2 or 3 items (forgot how many)
No analog to digital converter
An external power supply and power regulation circuitry is required (part of your isolator)
I have shown a full robot can be built for $50, so you would have to go below that
let us know on what you decide, I am curious . . .
besides, lawn mowing and snow shoveling is all part of the robot making process