Which Pi would be cheapest and funtional

[4ndy]

I know that this sounds like a dumb question but, what is the cheapest pi that I can use to make this work. What model should I purchase if i want to be able to have full functionality, including the Alexa mod. I am new to Raspberry pi, so please be specific. By full functionality, I mean, that It won’t be incredibly slow as well. Could I get a cheaper pi, missing one or two of the components, and just get a shield (is that what they are called with Pi’s?)?