Arhi posted v3 of an open source soldering station controller. Add an AC transformer from a cheap soldering station and you have a powerful pro-tool. Settings are entered by a rotary encoder dial, temperature and menu options are shown on a 16×2 LCD.
It works with most major soldering iron brands. Hakko (thermistor) or Solomon (K-type thermocouple) soldering pencils can be selected with jumpers. Replacement iron/handle assemblies are actually quote affordable (<$20), even quality stuff like Hakko.