Look into HTPCs. Barebone/mini computers are offered at Newegg. You'd essentially be looking for a nettop, or you can spend a little more to build a more future-proof system. I would recommend an Intel Atom-based system with NVidia ION graphics if you're going the nettop route. A more advanced HTPC would be on the level of i3 with Intel, or quad+ Phenom IIs with AMD. These days you can build a decent Intel-based HTPC for less than $400, but of course that is variable depending on your hardware choices.
Softsubs are one issue raised in the post above. Another problem, which is growing into a bigger and bigger one by the day, is the lack of 10-bit support on dedicated players.
So, while the price is probably cheaper for a simple MKV player, it is not versatile enough for a large portion of the content available on BBT. There is a chance that a nettop also cannot handle 10-bit decoding either, at least not smoothly, especially when you jump to the 1080p level.
