Is it worth getting an electric crockpot/slow cooker? Or will the electricity it will consume be too costly and offset the convenience?

There are crockpots that have low wattage.

a slow cooker is a good investment energy efficient and very convenient. Buy the removable one so it's easier to cook.

Logically, the amount of energy expended should be more for a slow cooker. Why? Because there are energy loses everywhere, from heat escaping from the pot (longer time, longer opportunity for heat to escape) to the natural resistance of the electric conduits. Whether it is worth the convenience depends on how much energy is lost x the cost of electricity.

We used to have one. Loved it because it gives us healthy food but gave it up because washing it became so inconvenient.

I agree with Ellie, I still have one, it was a novelty at first, but quickly became boring and inconvenient to wash. So it sits in the kitchen and I have to clean the dust off it......