Best Buy offers preorders of Sing on Blu-Ray / DVD / Digital HD bundled with an early release 4K Ultra HD digital download code for $19.99 with free shipping. That's the lowest price we could find for the Blu-ray alone by $4, excluding the below mentions. An email with instructions on how to redeem the early release download will be emailed within one hour of purchase. It's due for release on March 21.
A close price: Walmart charges the same, but without the download code. (Amazon has it for around the same with free shipping for Prime members.)