Well, we were strolling around the beautiful streets of Cascais and my friend said to me: I want an ice cream!
At the first cafe that we found we looked the prices of the ice creams and HUPS! They were more expensive than usually. Two steps forward we saw another cafe and the prices were just the same price as usually, so we bought there.
So, don't buy at the first place! The prices can rise in some places in summer time.
Cascais and Boca do Inferno are very touristy spots. This nice village becomes overcrowded on weekends as locals from surrounding areas come here to enjoy the views and the sun. So if you're planning to visit, try to do it during weekdays, as it could prove more advantageous to you.