I checked in adword tool and these are the monthy searches
mini smart tv: 720 global searches
smart tv: 1,830,000 global searches
So my guess is "mini smart tv" is a sub category so I see it a bit limited as to be a good idea to build a site specialized, so no, I don't see it interesting, I think people would prefer go with a broader option like the term "smart tv" for example
I'd say: $20 - $100
Just my 2 cents, I hope I was wrong
Good luck