I don't know of any BDUs that have SD only boxes available. Almost all modern video equipment is HD capable with backward compatibility for SD and costs no more than SD equipment did 10 years ago. It might be possible to find a used SD box but it would lack features and channels plus it's reliability, compatibility and suitability for future use would be questionable. So why bother?
Similarly, wiring for video is archaic and expensive compared to a BDU supplied remote STB or a cheap, supported media player or such as a Fire TV stick. A good quality 50' HDMI cable alone costs about $50 and that doesn't include the cost of installation and extra equipment such as an HDMI splitter and additional issues such as a remote control extender. It may even affect the resale value of your home. Cheap wireless HDMI repeaters are often unreliable and good ones are expensive so trying to extend HDMI that way is also a questionable exercise compared to using a supported wireless device.