In Europe most TV's come with SmartTV functionality. I don't see a big price difference between TV's with or without SmartTV module. Actually it is probably quite difficult to find a TV without it.
Pricewise you can right now purchase a Hitachi 43" TV with UHD resolution and SmartTV functionality for 355 Euro. It doesn't get cheaper than that...
Regarding separate Android boxes: most of them are cheap, including the Raspberry Pi used with OpenELEC and XBMC/KODI.
*** But IMHO all of them suck. ***
There, I said it. They suck as much or even more than the SmartTV modules in the TV's.
Plus: Nothing comes close to having just one TV in front of you, one remote and even the wife is able to go to the movies folder of the network PnP server and pick a movie.
With an external box, you have to:
a) turn it on
b) wait for it to boot
c) change input on TV
d) grab the other remote
e) hope that everything is working
And most devices I have tested are slowwwww.
I have an LG and a Samsung, both with SmartTV module. Much nicer to watch movies in PnP network.
Browser, Youtube, etc.? Slow like hell and text input is a pain.
But for that I use my tablet, smartphone or PC.
Cheers,
Vitor