The Roku Premiere + Plus is on sale for $49.99 with free shipping (tax might be addl) at Walmart.com. This is model 4630RW, which has 4K and HDR (if your tv supports it), and includes a headphone jack on the remote (for private listening).
This is the cheapest I found for a non refurbished, non-YMMV. It might go on sale further in the next couple weeks, but you may be able to price match/ return if necessary if the price drops.
If you want to check brickseek for any leftover stock in your area for even cheaper:
Roku Premiere+ (2016 Model)
Full specs are available here: