Best Buy is offering build-your-own combo discounts with purchase of "select PCs" and Microsoft Mixed Reality kits. This is a different offer than the HP and Dell combos that are currently FP. The offer says "up to $200 off" but is ringing up the $399 Acer, Lenovo, HP and Dell kits for free, and the $499 Samsung kit for $99.
There are a bunch of Alienware machines, the Dell Insprion 15, and an Asus RoG laptop eligible for this offer.
Pick a PC, pick a headset, and add offer to cart. Headset should show up at the free/discounted price.
Update: Offer now says "up to $500 off" so doesn't look like a mistake.