However i like to think of it in this way:
Perspective: The point of view from which something is looked at
Mental Model: A mechanism or thought pattern to make sense of something or understand something about some situation
You can never break out of your perspective of looking at the world. So a mental model is always confined within a specific perspective.
Example:
Supply&Demand is a model that helps you understand pricing in markets. The point of view/perspective is that of an economics/economist perspective. You could just as easily look at the same situation from a different perspective such as sociology or even psychology.
In other words, mental models are like a short cut to look at situations, solve problems and understand the world from different perspectives.