805x devices with internal converters are quite inexpensive. Serial DAC's are inexpensive. POT's are expensive. Passive components suitable for any sort of precise use are VERY expensive.

The most common process for this sort of thing is to establish operating requirements and limits before deciding on a microcontroller or on peripherals for it.

You've got to include information such as how quickly the converter has to settle, the precision, etc. That's why people don't know what to tell you. If you need very little precision, you can probably build a converter from a port and some resistors, but if you need precision, you need resistors that cost more than your controller.

RE