I think I'll get a cheap $10 temperature logger and try and do a conversion to voltage for fun.
There is quite a large market for temperature loggers (storage and shipping of foodstufs, medicines, etc), so they are mass produced and cheap. They are generally not hackable in any useful way.
There is a small market for low/medium accuracy voltage loggers... either single- or multi-channel. so they're less common and relatively expensive.
Most applications involving voltage measurement will require higher precision, or have more complex requirements (voltage ranges, interval, programmability), so something more expensive or custom will be required. I use a PC with a LabJack for most of my data logging on the bench. I've also put together custom loggers using a Teensy or an Adafruit Feather (as suggested by maxwell3e10).