If you're alright with a bit of suffering in exchange for large savings, I'd recommend checking out Android boxes to import from China, then. At work we bought a batch of one called Nexbox A95x, which is the size of a waffle, barely heavier than one yet leaves most RPi's in the dust spec-wise, and as bonus it's cheap as dirt: US$40 plus shipping, IIRC. Problem is, they come with Android out of the box, so if you want absolute control you'd have to flash them with the ARM port of Debian or similar; hence the "suffering" part.

The advantage of the RPi is the huge number of accessories and documentation for it (for instance, for building your own enclosures), but if you're not interested in that or hooking up a thermal printer and a remotely-controlled camera to your set-top box, you should really look into it.