Amazon is offering a $100 Amazon GC with the purchase of a Google Pixel 3a, 64 GB for $399. It is shipped and sold by Amazon.com. The offer seems to only work with the color Just Black or the Purple-ish. I believe it is unlocked because no carrier info is associated with the listing.
***You MUST ADD the $100 Amazon GC to your CART. Click the link under the price on the description page.***
I assume it is on backorder because it says it will ship in 1-3 weeks.