Trying to create a definitive line between Mid Fi and Hi Fi is a fools errand. At best I may consider the following... 1. The listeners intention, and 2. The type of equipment being assembled. Cost of equipment is not a determining factor in my opinion. As far as intension goes, if you are assembling a system for the purpose of listening to music and during this process you are making decisions to the components used to produce the most life like reproduction, then I would consider what you assembled to be a Hi Fi system. Now, and this is where I get to my second point, you are just purchasing an all in one component (say a BT speaker) this doesn't qualify as Hi Fi to me.
I've had people over my house who have been amazed by my outdoor speaker pods playing on my deck with a subwoofer that looks like a rock in my yard. Then I bring them into my home to listen to my very modest Hi Fi system and they are just blown away. The same thing seems to happens to most people when I show them my Hi Fi system. They go from just casually hearing the music to actually listening to the music. Suddenly they are aware of the soundstage, the instrument placement in front of them, the ambient sounds in the recording like fingers sliding up guitar strings and the singer taking a breath while he's singing. When you assemble a system that produces that detail, it drags most people in. A Beats Pill isn't going to do that...